Common bed bug Cimex lectularius, photographed by Piotr Naskrecki.

Belongs within: Cimicomorpha.
Contains: Cimex (Oblongus), Cimex (Rotundatus).

The Cimicidae, bed bugs, are a group of flightless, flattened bugs that feed on blood from mammals and birds. The best known species is the common bed bug Cimex lectularius, a notorious pest in human dwellings. Other species known to parasitise humans are C. rotundatus and Leptocimex boueti (Askew 1971).

Love hurts
Published 3 July 2007

People generally know distressingly little about insects. The gossip section of the weekly telly guide with the paper on Saturday mentioned a comment by Jerry Seinfeld on an upcoming movie of his featuring bees: “Other insects are just kind of crawling around. They don’t have the sophistication of the bee. They have no crime, they have no drugs, they have no rape. A little rape, but it’s not that bad.” Leaving aside the question of the propriety of these comments, I have one word to say about their accuracy: bedbugs. Welcome to the world of Traumatic Insemination.

Male bedbugs (Cimicidae) have a sharpened intromittent organ (or if you prefer, a great spike on their knob). The usual means of entry is ignored in mating—rather, the female genital tract is only used in egg-laying (Stutt & Siva-Jothy 2001). Instead, the male uses his sharpened organ to pierce through the female’s body wall and inject semen directly into the body cavity.

Males and females do not always have the same aims in sexual reproduction. Because the limits on reproduction rates for males are relatively minimal, it is generally in the interest of males to maximise their insemination rate, in order to maximise the number of offspring they produce. Females, on the other hand, are more likely to have a maximum reproductive rate limited by the number of offspring they can safely produce in a given time period. Therefore, it is more advantageous for them to limit fertilisation to the best males to maximise the health of their offspring. As well as the obvious restrictions a female can place on fertilisation by limiting the ability of males to mate with her, the genital tract of females often has adaptations to ‘test’ sperm. The genital tract itself may be hostile to sperm survival (by being highly acidic, for instance). There may be structures such as a bursa copulatrix that store and/or digest sperm, limiting their access to further parts of the tract.

It is suspected that traumatic insemination evolved in males to bypass these restrictions on the part of the females. A good demonstration of this is seen in bugs of the family Nabidae, where entry into the female is still by the genital tract, but the sharpened intromittent organ pierces the wall of the bursa copulatrix (Tatarnic et al. 2006). Experimental evidence has shown that in traumatic inseminations the fertilisation advantage is held by the last males to mate with a female (Stutt & Siva-Jothy 2001).

Nevertheless, females are not without defenses. While female bedbugs show a surprising lack of behavioural defenses against mating, they have developed an entirely novel paragenital system called the spermalege. In the common bedbug (Cimex lectularius), the external part of the spermalege is a special notch and a thickened part of the cuticle. Internally, there is a pocket filled with cells that receives the male ejaculate. Morrow & Arnqvist (2003) demonstrated that traumatic insemination through the spermalege had relatively little effect on the health of the recipient females. However, if the body wall was pierced anywhere else the female’s survival rate was severely compromised. The internal part of the spermalege probably fulfils the sperm-killing role of the usual genital tract, as well as reducing the direct exposure of the female body cavity to potentially harmful ejaculate (Morrow & Arnqvist 2003).

Different genera of bedbugs show a wide range of variation in the complexity of the paragenital system, from species entirely lacking one to species in which the system is exceedingly complex. In at least one genus, Afrocimex, a spermalege is present in both males and females (Tatarnic et al. 2006). It has been suggested that the presence of a spermalege in males defends against damage from homosexual matings—male bedbugs apparently tending to stab first and check suitability afterwards.

Systematics of Cimicidae

Characters (from Carver et al. 1991): Body oval, flattened; clypeus apically expanded; pronotum anterolaterally and laterally expanded; forewings reduced to transverse scales.

|--Stricticimex brevispinosusCGW91
|--Leptocimex bouetiA71
|--Oeciacus hirundinisRD77
|--Haematosiphon inodorusRD77
|--Canthecona cyanacantha Stal 1870K08
| |--P. biguttula Haglund 1868K08
| `--P. metaphaea (Walker 1867) [=Cuspicona metaphaea]D00
|--Lamprophara bifasciata [incl. L. bifasciata var. quadrifera]K08
| |--C. bergrothianus Kirkaldy 1908K08
| |--C. fungicola Kirkaldy 1908K08
| `--C. hochstetteriK08
`--Cimex Linnaeus 1758L58
| i. s.: C. bimaculatus Linnaeus 1758L58
| C. columbariusA71
| C. dolabratus Linnaeus 1758L58
| C. erraticus Linnaeus 1758L58
| C. ferus Linnaeus 1758L58
| C. incrassatusBVP96
| C. laevigatus Linnaeus 1758L58
| C. mutabilis Linnaeus 1758L58
| C. populi Linnaeus 1758L58
| C. rotundatus [incl. C. hemipterus]RD77
| C. striatus Linnaeus 1758L58
| C. sylvestris Linnaeus 1758L58
| C. ulmi Linnaeus 1758L58
|--C. (Apterus Linnaeus 1758)L58
| `--C. (A.) lectularius Linnaeus 1758L58
|--C. (Coleoptratus Linnaeus 1758)L58
| |--C. (C.) clavicornis Linnaeus 1758L58
| |--C. (C.) littoralis Linnaeus 1758L58
| `--C. (C.) rugosus Linnaeus 1758L58
|--C. (Linearis Linnaeus 1758)L58
| |--C. (L.) coryli Linnaeus 1758L58
| |--C. (L.) lacustris Linnaeus 1758L58
| `--C. (L.) vagabundus Linnaeus 1758L58
|--C. (Membranaceus Linnaeus 1758)L58
| |--C. (M.) betulae Linnaeus 1758L58
| |--C. (M.) cardui Linnaeus 1758L58
| |--C. (M.) corticalis Linnaeus 1758L58
| |--C. (M.) erosus Linnaeus 1758L58
| `--C. (M.) filicis Linnaeus 1758L58
|--C. (Oblongus)L58
|--C. (Rotundatus)L58
|--C. (Scutellatus Linnaeus 1758)L58
| |--C. (S.) arabs Linnaeus 1758L58
| |--C. (S.) lineatus Linnaeus 1758L58
| |--C. (S.) serratus Linnaeus 1758L58
| |--C. (S.) stockerus Linnaeus 1758L58
| `--C. (S.) stolidus Linnaeus 1758L58
|--C. (Seticornis Linnaeus 1758)L58
| |--C. (S.) annulatus Linnaeus 1758L58
| |--C. (S.) ater Linnaeus 1758L58
| |--C. (S.) gothicus Linnaeus 1758L58
| `--C. (S.) personatus Linnaeus 1758L58
|--C. (Spinipes Linnaeus 1758)L58
| |--C. (S.) abietis Linnaeus 1758L58
| |--C. (S.) calcaratus Linnaeus 1758L58
| `--C. (S.) kermesinus Linnaeus 1758L58
`--C. (Spinosus Linnaeus 1758)L58
|--C. (S.) acantharis Linnaeus 1758L58
|--C. (S.) bidens Linnaeus 1758L58
|--C. (S.) bipustulatus Linnaeus 1758L58
|--C. (S.) haemorrhoidalis Linnaeus 1758L58
|--C. (S.) marginatus Linnaeus 1758L58
|--C. (S.) punctatus Linnaeus 1758L58
|--C. (S.) quadrispinosus Linnaeus 1758L58
|--C. (S.) rufipes Linnaeus 1758L58
|--C. (S.) valgus Linnaeus 1758L58
`--C. (S.) ypsilon Linnaeus 1758L58

*Type species of generic name indicated


[A71] Askew, R. R. 1971. Parasitic Insects. Heinemann Educational Books: London.

[BVP96] Batalla, I. B., M. Vargas & O. J. Polaco. 1996. Arthropods associated with Myotis thysanodes Müller 1897, in San Josecito Cave, Nuevo Léon, México. In: Mitchell, R., D. J. Horn, G. R. Needham & W. C. Welbourn (eds) Acarology IX vol. 1. Proceedings pp. 109–111. Ohio Biological Survey: Columbus (Ohio).

[CGW91] Carver, M., G. F. Gross & T. E. Woodward. 1991. Hemiptera (bugs, leafhoppers, cicadas, aphids, scale insects etc.) In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 1 pp. 429–509. Melbourne University Press: Carlton (Victoria).

[D00] Distant, W. L. 1900. Rhynchotal notes.—IV. Heteroptera: Pentatominae (part) (concluded). Annals and Magazine of Natural History, series 7, 5: 420–435.

[K08] Kirkaldy, G. W. 1908. A catalogue of the Hemiptera of Fiji. Proceedings of the Linnean Society of New South Wales 33: 345–391, pl. 4.

[L58] Linnaeus, C. 1758. Systema Naturae per Regna Tria Naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Laurentii Salvii: Holmiae.

Morrow, E. H., & G. Arnqvist. 2003. Costly traumatic insemination and a female counter-measure in bed bugs. Proceedings of the Royal Society of London Series B—Biological Sciences 270: 2377–2381.

[RD77] Richards, O. W., & R. G. Davies. 1977. Imms’ General Textbook of Entomology 10th ed. vol. 2. Classification and Biology. Chapman and Hall: London.

Stutt, A. D., & M. T. Siva-Jothy. 2001. Traumatic insemination and sexual conflict in the bed bug Cimex lectularius. Proceedings of the National Academy of Sciences of the USA 98 (10): 5683–5687.

Tatarnic, N. J., G. Cassis & D. F. Hochuli. 2006. Traumatic insemination in the plant bug genus Coridromius Signoret (Heteroptera: Miridae). Biology Letters 2: 58–61.

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