Although initial box office reception was positive both in the United Kingdom and overseas, Inseminoid has since failed to impress a majority of critics, who have faulted Warren's film for perceived poor acting, special effects and set design. Despite praise for actress Judy Geeson's depiction of the lead character, Sandy, approval of the film in general has been tarnished due to its concept of an extraterrestrial insemination, which has been viewed negatively in comparison to the premise of Alien (1979). Both Warren and Alien distributors 20th Century Fox have rejected claims that the script of Inseminoid was influenced by that of the earlier film.
On a desolate planet, a team of 12 Xeno project scientists are conducting an archaeological excavation of the ruins of an ancient civilisation. Shortly after an underground tomb network is found to contain crystals and wall inscriptions, photographer Dean White (Dominic Jephcott) is engulfed in a rock blast and left incapacitated. Deciphering the alien language in the caves, xenolinguist Mitch (Trevor Thomas) theorises that the civilisation was built on the concept of dualism: the planet orbits a binary star, and a pair of twins seems to have ruled the race that once inhabited it. Medical assistant Sharon (Heather Wright) discovers that an energy field surrounds the crystals, which causes her to deduce that a "chemical intelligence" controlled life on the planet.
A mentally unbalanced Ricky Williams (David Baxt) is driven to re-enter the caves when a sample of crystals pulsates and the chemical intelligence exerts its influence through a mark on his arm. Thrown into a grille in a compromised environmental suit, Gail (Rosalind Lloyd) removes her helmet and freezes to death in the toxic atmosphere while trying to amputate her trapped foot with a chainsaw. Documentation officer Kate Frost (Stephanie Beacham) shoots Ricky with a harpoon gun before he opens both the inner and outer airlock doors and renders the air inside the base unbreathable.
Following the burial of Ricky and Gail, Mitch and Sandy (Judy Geeson) return to the caves to collect more crystals. A monstrous creature appears and dismembers Mitch before raping Sandy. Found distraught, Sandy receives treatment from Sharon and chief medical officer Karl (Barry Houghton), who discovers that the assault has triggered an accelerated pregnancy despite the regular intravenous injections of contraceptives given to the women in the team. When further explosions within the catacombs scupper chances of deeper investigation, the surviving members of the team are left with nothing to do but await the arrival of a Xeno rescue shuttle.
The intelligence assumes control of Sandy, who has been marked in the same way as Ricky. She stabs Barbra (Victoria Tennant) to death with a pair of scissors, demonstrating superhuman strength while committing the murder, and then mutilates Dean and the remains of Mitch, drinking their blood. The rest of the team seek refuge in the Operations Room as Sandy destroys essential machinery – including the base transmitter – with explosives. When the imbalance in Sandy's mind appears to correct itself, Karl, Sharon and Commander Holly McKay (Jennifer Ashley) attempt to sedate her to spare the unborn children. Sandy's madness returns and Holly and Karl are killed in an accident with heat-sealing apparatus, whereupon Sandy disembowels the corpses.
Senior officer Mark (Robin Clarke) radios Sandy – his romantic interest – from the Operations Room to stall for time as Kate and operations chief Gary (Steven Grives) depart to requisition chainsaws from a storage room. The ruse is uncovered and Sandy harpoons Gary outside the airlock, breathing the atmosphere to no ill effect as she mauls his flesh. Preparing for a final confrontation, Mark stumbles across Sandy's newborn, mutant twins. He entrusts them to Sharon as the mother blasts through the Operations Room door and destroys all the equipment inside, although it is evident that she no longer possesses unnatural strength. Crippled by an explosive charge, Kate is gored to death. In a last stand, Mark strangles and kills Sandy with a ripped-out cable. He returns to Sharon to discover one of the twins biting at her slit neck, before its sibling launches itself at him.
Twenty-eight days later, Xeno Auxiliary Module 047 lands on the planet to investigate the loss of contact with the team. With the base in ruins, the mission records destroyed and the scientists either murdered or missing, combat marksmen Corin (Kevin O'Shea) and Roy (Robert Pugh) abandon the search for survivors and pilot Jeff (John Segal) contacts Xeno control to request clearance to return. The final shots reveal that Sandy's children have stowed themselves away inside a storage compartment on board the shuttle.
Following the releases of Satan's Slave (1976), Prey (1978) and Terror (1979), Norman J. Warren had at first been attached to direct a film titled Gargoyles. When this production collapsed at the scripting stage, Warren and his producer, Richard Gordon, accepted a plot proposal from the husband-and-wife team of Nick and Gloria Maley, who had worked on Satan's Slave as members of the special effects department besides Star Wars (1977) and Superman (1978). The Maleys drafted their concept as a composite of their favourite science-fiction ideas and an opportunity to exhibit their best effects work, although the suggested title, Doomseeds, had to be changed to avoid confusion with the 1977 film Demon Seed. The script for the new Inseminoid, which indicates that the film is set two decades in the future in a militaristic universe, required amendments prior to filming, although the premise received Warren and Gordon's approval.
Producer Richard Gordon cast American actors Clarke and Ashley while on business in Hollywood. Prior to Inseminoid, Ashley had starred in minor films of such independent studios as Crown International Pictures, while Clarke had just completed filming on the 1980 film The Formula. Warren recalls that although Ashley "was not the greatest actress, she was very enthusiastic and very easy to work with." The professional relationship between Warren and Clarke broke down during the filming of sequences such as Dean's incapacitation inside the caves, when the director and actor disagreed about the extent to which Clarke needed to respond to the script when his character raises his voice to a shout. Warren asserts that Clarke's "high opinion of himself" made the actor "a nightmare to work with", and adds that he "could be extremely difficult, making every scene with him an uphill struggle."
Rapports between the director and other cast members proved to be positive: in particular, Geeson is credited as "an absolute dream to work with" and praised for her acting of the maddened expectant mother, which Warren argues avoids descending into unintentional humour. Gordon also offers a positive assessment, stating that Geeson accepted the demands of her part with enthusiasm and did not complain that it demeaned her as an actress.
Warren retains fond memories of Beacham's "very professional" performance, and remarks that, "with tongue firmly in cheek, she would often wind me up by asking what her motivation was for a particular action, just as I about to call 'Action!', knowing full well that my answer would be, 'Because it's in the script'." Beacham, a mother of two infant children, agreed to appear in the film to support her family: "I had to choose between a play that I really, really wanted to do, which would have paid me £65 a week, and this script for a film called Inseminoid. Hey! No choice. Two pink babies asleep upstairs! No choice!"
Agreeing to fund half of the proposed £1 million budget, the Hong Kong Shaw Brothers became partners in the film's production. Elder brother Sir Run Run Shaw is credited as the presenter of Inseminoid in the opening titles. With a production staff of 75, principal photography commenced on 12 May 1980. John Metcalfe, camera operator for Satan's Slave and Terror, assumed the role of cinematographer. His former role fell to the less experienced Dick Pope. Three weeks of location filming at the Chislehurst Caves in Kent preceded a one-week indoor session at Lee International Studios at Wembley Park in London. The second unit completed special effects and linking shots in a fifth week, based at Film House in Wardour Street. To simulate the desolate landscape of the alien planet in long shots, the production team departed for the island of Gozo off Malta for a final shoot of two days, capitalising on the strong Mediterranean sun to produce good lighting.
Opting to shoot using Mitchell cameras incorporating 35 mm Eastman Kodak film and anamorphic lenses, Warren recalls that the produced footage boasted "an incredibly sharp image and what I would term as the 'American' look." He remembers that the setting of the Chislehurst Caves rendered the subterranean complex more realistic than a potential in-studio alternative given the modest budget of Inseminoid. However, the cold, damp, airless conditions, combined with the uneven surface of the cave floors, complicated the filming sessions and necessitated frequent repairs of equipment.
Shooting often ran for 12 hours at a time and led to frequent minor injuries among the cast and production staff, while some developed intense feelings of claustrophobia in the confined space. Gordon suggests that the uncomfortable working conditions made the performances of the cast more realistic, but concedes that although, "I think all this paid off in terms of what we got on the screen for the budget, but the circumstances were very difficult." In the absence of suitable facilities inside the caves, the personnel established administrative, dressing and make-up rooms in a car park some distance from the filming area. Co-writer Nick Maley reprised his role as a special effects technician to produce the infant twin props that appear in the climax of the film.
The filming of Inseminoid wrapped two days behind schedule. Warren remembers making a major cut to scenes of Ricky's rampage to help the shooting finish on time: "I had to put the "blue pencil" through part of the scene, which involved a chase through various tunnels. Three pages of script, which I had to condense into one shot. Having to make such an enormous compromise was not a happy choice for me, but it was the only way of getting us back on schedule." On his contribution to Inseminoid, Warren stated that Peter Boyle proved to be "a pleasure to work with, because he had a natural feel for the material and managed to create just the right pace and rhythm throughout the film." During the post-production process, the editing staff increased the brightness of the original print, concerned that a dim appearance would damage the chances of sales to television broadcasters, and removed the most graphic shots of the birth of the mutant children for the purposes of classification. The opening title visuals, consisting of vibrant oil frames, are a contribution of Oxford Scientific Films.
Determining that the low budget precluded an orchestral soundtrack, Warren and his long-serving composer, John Scott, agreed that all the music should be electronic. Produced after hours of studio multi-tracking and overdubbing, Warren considers the final score an "amazing achievement" and praises Scott's realisation of a soundtrack incorporating the "experimental" electronic brand of music. The score received an LP release in 1982.
In the UK, Inseminoid premiered on 22 March 1981 in the Midlands. It later opened at 65 cinemas in the region, and reached London in October. Overseas, German cinemas had begun to exhibit the film in January under the title Samen des Bösen (English: Seeds of Evil). To the dislike of Warren, distributors Almi released the film under the title Horror Planet in the United States and Canada, but later restored the name to the original Inseminoid.
Original pre-release advertising included a regional "mail drop" of circulars presenting screenshots of a screaming Geeson and the tagline "Warning! An Horrific Alien Birth! A Violent Nightmare in Blood! Inseminoid at a Cinema Near You Soon!" Warren, who regrets the decision to publicise the film in such a graphic manner, comments, "The problem with mail-drops is that you have no way of knowing who lives in the house, or who will see it first. It could be a pregnant woman, and old lady, or even worse, a young child. So it was not such a good idea."
Rated "X" in the UK, in the United States Inseminoid screened under the "R" certificate for its "profanity, nudity, violence, rape and gore". In 2005, the British Board of Film Classification revised its certification of Inseminoid, re-rating the film "15" from "18" for its "strong, bloody violence". Inseminoid became one of the first films to be released on VHS soon after its appearance in cinemas, and reached seventh position in British video sales charts in November 1981. Renewed editions became available in 1992 and 1998.
Inseminoid attracted positive critical reception on its original release. In terms of box office performance, it reached a high of fifth position in the 1981 British charts. At one point it ranked seventh at the box office in France, while in the United States it proceeded to enter the Los Angeles Times list of top ten films. American director Roger Corman congratulated Warren on the film and considered commissioning him for further productions. However, a private screening had failed to impress members of the British Academy of Film and Television Arts, who dismissed Inseminoid as "'Commercial rubbish! ... Not the sort of thing the Academy should be showing ... And certainly not the kind of film the British film industry should be making!'"
In 1982, Inseminoid received a minor accolade at the Italian Fantafestival (winning the Best Special Effects prize) and a nomination at the Fantasporto convention in Portugal (for the Best Film award). Recalling how the depiction the female sex in Inseminoid displeased women's circles, Warren states, "It seems it is quite common for pregnant women to have nightmares about giving birth to some kind of monster. Of course, all their complaints and their letters which were printed in the local papers only helped to increase the queue at the box office."
Examining the acting in a review published in Starlog magazine, Alan Jones expressed a preference for the British members of the cast, crediting Geeson as "absolutely first-rate" and criticising "the weak performances from the token Americans, Robin Clarke and Jennifer Ashley". Praising the production values for cost-effectiveness, he discerned signs of Warren's "particular trademark" in such murder scenes as that of Barbra (through repeated scissor-stabbing) and Holly (through heat-searing). He professed his opinion that Inseminoid "is not faultless by any means", citing a predictable and often "ridiculous" plot as factors detracting from his pleasure in viewing the film. Nevertheless, he asserted that Inseminoid meets audience demands for a B film of its genre, progressing "at such a pace that you nearly almost forget that you've seen it all before", and declared it to be "far less routine and far more enjoyable than I had expected."
Critical response in the United States proved to be less favourable. In a review published in Virginia in January 1983, Edward Jones of The Free-Lance Star offered praise for the "novel touch" of casting a would-be-mother as the principal villain, commenting, "In what has to be a new low, even for extraterrestrial-horror films, all the men end up punching this pregnant woman in the stomach. What a time to have twins!" Nevertheless, Inseminoid is discarded as "no more than a mix of everything-you've-ever-seen-in-a-horror-movie-and-didn't-particularly-want-to-see-again." In a November 1983 edition of the Floridian newspaper Boca Raton News, Skip Sheffield branded the film "horrible" and "cheapo", suggesting that his readers "Imagine Alien without the fantastic sets, convincing special effects and literate dialogue, and you have a picture of Horror Planet." He added his opinion that brutal violence does not guarantee narrative suspense, punning on the name Run Run Shaw in his downbeat conclusion that "Horror Planet is a film to run, run away from—fast."
In 2004, Douglas Pratt argued that Inseminoid consists of "some gooey gore shots but few other thrills" and denounced the quality of the acting and props used. He still conceded that Inseminoid "goes through the motions properly, however, so fans will probably find it worth passing the time." The film is award one star out of five on the AllRovi website, where reviewer Cavett Binion rules that it is a "fairly standard rip-off" of Alien in spite of the originality of its core premise, with a "rabid, eye-popping performance" from Geeson that is "more than a bit uncomfortable to watch." The rape sequence is seen as a "surreal and truly disgusting flashback" and the title of the film itself deemed "sleazy".
Warren rejects the label "video nasty", which has been applied to Inseminoid on the incorrect assumption that its violent content made it impossible to release uncut on home video formats in the UK. The film was incorrectly labelled as previously banned in 1984 when it was rereleased in its cut cinema print in 1994 by Vipco. It has long been uncut in the UK on DVD. In response to the idea that the film has attained cult status, he remarks, "if Inseminoid has become some form of cult movie, then I am very pleased and, indeed, very flattered." On his private response to his work, he answers that "I don't think you could ever be one hundred percent satisfied with any film you make", and that, in the scenario of remaking Inseminoid, he would darken the lighting of certain scenes to heighten the tension and demand a longer filming schedule.
Inseminoid has been criticised as a perceived imitation, "knock-off" or "rip-off" of the 1979 science-fiction horror film Alien. Peter Wright, a film historian and lecturer at the University of Liverpool, interprets both the "atmospheric" scenes set in the underground tomb network, and the mess hall sequence preceding Rick's madness, as potential derivations from Ridley Scott's film: while the first recalls the setting of the remote planetoid, LV-426, the second resonates with the "chestburster" horror scene. Wright asserts that the connection of Inseminoid to Alien could appear to be "exploitative", while Barry Langford of the University of London views Inseminoid as representative of the dependence of British cinema on its American counterpart.
Alan Jones of Starlog magazine suggests that "any similarity between Inseminoid and Alien is totally intentional. Except here is the basic idea contained in Alien taken to its sleaziest extreme." He interprets one such parallel in the character of Kate who, it is argued, emulates the appearance of Sigourney Weaver in the role of Ellen Ripley. However, he also cites Contamination (1980) and Scared to Death (1981) as less effective imitations of Scott. Besides Alien, Edward Jones of the newspaper The Free Lance–Star discerns elements of the novel Dracula (1897), the TV series The Bionic Woman (1976–78), and the films Night of the Living Dead (1968) and The Thing (1982) in the plot of Inseminoid.
Warren denies claims of an imitation, noting the discrepancies between the production schedules: when Inseminoid entered the shooting stage, Alien, which had been filmed in closed studios, had been released months before. While the director accepts the often "uncanny" similarities between the two films, he states that Alien distributors 20th Century Fox discounted the possibility of derivation after watching the final cut of Inseminoid: "... in fact, the head of Fox sent us a very nice letter saying how much he enjoyed the film and wished us luck with the release ... I find it flattering that anyone can compare Alien, which cost in the region of $30 million, with Inseminoid which cost less than £1 million. We must have done something right."
Wright interprets the transformation of Sandy from innocent female to a murderous mother-to-be of human-alien hybrid twins as a "direct manifestation of masculine anxiety regarding female reproductive capacity". He comments that the origin of the horror of Inseminoid is internalised as the seed of a violent alien life form, which renders Sandy "woman-as-other", or "abject Other". This opposes the transferring of "fear of woman onto the alien other" as demonstrated in the extraterrestrial villain of Alien. Inseminoid is also judged to be reminiscent of the 1977 film Demon Seed, which casts an advanced computer as the source of a rape resulting in insemination: "in both films, women are framed as 'Other' by their sexual congress with more conventional iconic others: the machine and the alien." Pregnancies are depicted as sources of horror, an attitude apparent in the "uterine and cervical" opening credits of Inseminoid, which are suggestive of the viewer "entering the realm of the monstrous womb ... the titling reveals a microscopic insect resident in the body of a larger organism."
Wright argues that Warren's inspiration of terror through a distorted representation of the uterus strikes a chord with the 1979 film The Brood, in which a woman produces deformed children through asexual reproduction. Commenting further, he examines the rape sequence itself, in which Sandy witnesses Karl injecting her with an unknown substance prior to the alien insemination, and makes a connection to dialogue from other scenes indicating that the female Xeno scientists are regularly administered intravenous injections for contraceptive purposes. The impregnation of Sandy through perverted intercourse, conflicting with the suppression of childbirth that is manifested through Karl's use of a hypodermic and (phallic) needle, reveals "coherent sexism" in so far as Inseminoid "attacks the very notion of female sexual freedom, while suggesting, paradoxically, that contraception is the responsibility of women." That Sandy reproduces at an accelerated pace and regresses into an animalistic state are factors adding to her depiction as an abject Other, or object of "male paranoia".
During the final struggle, which pits the patriarchal social structure of the Xeno team against Sandy's maternal element, it is not until Gary has half-suffocated in the toxic atmosphere that he is murdered. Wright argues that the sequence is reassuring from a male perspective despite its graphic content, since it implies that no woman, even one with superhuman strength, possesses the power to kill a man in cold blood. A murderer of colleagues of both sexes, that Sandy dies at the hands of Mark ultimately renders her an aid to the re-empowerment of the male sex, although the twin offspring are quick to avenge her. Comparing the plot of Inseminoid to Biblical scriptures, Christopher Partridge of Lancaster University turns his attention to the nature of the twins, referring to them as "essentially space Nephilim, technological demons with appetites and habits reminiscent of the mythic forebears."
Maternal images endure as far as the epilogue, featuring the arrival of Jeff, Corin and Roy at the Xeno base. In an allusion to the human menstrual cycle, it is said that 28 days have elapsed since the communications break-down. The destruction of the installation and the deaths of its personnel are attributed to an "internal disturbance of some kind", forming "an ironic phrase which encapsulates the film's vision of pregnancy as an irruption of Otherness from within." Focusing on Larry Miller's 1981 novelisation, described as "imaginative and misogynistic", Wright refers to sequences that are absent from the film and inspire repulsion on the part of the reader at the distortion of the female form. New transformations that afflict Sandy include oozing sores (which Wright construes as an aberration of natal oil secretion) and pus emanating from the nipples (argued to mirror colostrum, or pre-milk). Sandy accepts such unnatural metamorphoses, which culminate in the onset of labour, with fascination.