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Species of various insect orders possess specialised tarsal adhesive structures covered by a thin liquid film, which is deposited in the form of footprints. This adhesive liquid has been suggested to be chemically and physiologically related to the epicuticular lipid layer, which naturally covers the body of insects and acts as the prime barrier to environmental stresses, such as desiccation. The functional efficiency of the layer, however, is jeopardised by partial melting that may occur at physiological temperatures. In this study, light microscopic images of elytral prints show that the epicuticular lipid layer of the Colorado potato beetle Leptinotarsa decemlineata actually is partially liquid and chemical investigations reveal the high similarity of the epicuticular hydrocarbon pattern and the tarsal liquid. By means of chemical manipulation of the surface hydrocarbon composition of live beetles, the substance exchange between their tarsal adhesive hairs and the body surface is monitored. Histological sections of L. decemlineata tarsi, furthermore, reveal glandular cells connected to individual adhesive setae and departing from these results, an idea of a general mechanism of tarsal secretion is developed and discussed in a functional-ecological context.

Complex genitalia are ubiquitous among arthropods, but little attention has been given to the fact that the evolution of such elaborate structures may have led to biomechanical constraints that hinder their usage. In the rove beetle, Aleochara tristis, the male's intromittant organ consists of a long flagellum that is more than twice the body length. It is introduced into the spermathecal duct of the female during copulation. The flagellum apparently functions as a guiding rod for a tube growing from the spermatophore that the male deposits in the female's genital chamber. The extraordinary length of the intromittant organ poses a unique physical challenge for the male. During its retraction from the female after mating, the flagellum is under considerable tension. Any sudden release of this tension would result in the flagellum becoming severely entangled, preventing the male from mating again. In response to this novel physical challenge, males have apparently evolved a specialized behavioural adaptation that prevents entanglement after copulation. While retracting the flagellum from the female, the male secures it between a wing shoulder and the pronotum ('shouldering'), holding it taut for about one half of its length. This allows the stepwise retraction of the flagellum from the female and allows it to be retracted back into the male's body in an orderly fashion. This is, to our knowledge, the first demonstration of a behavioural adaptation that has evolved to ameliorate the biomechanical problems caused by exaggerated genital morphology.

Most studies on insect sperm motility have been conducted in vitro using artificial environments outside the animal's body. Only little is known about the function of motile insect sperm at different sites within the male or female genital tracts. We dissected genital tracts of female rove beetles (Drusilla canaliculata) to show that spermatozoa use their own motility to migrate from the spermatophore into the spermatheca. Our dissection method allowed direct observation and filming of the spermathecal filling process inside the female's genital tract. Spermatozoa were found to enter the spermatheca individually, sometimes in groups of two or three. Although exhibiting only weak motility and no progressive motion in buffer solution, the spermatozoa inside the female show vigorous lashing and reach an average velocity of 47.5 microm s(-1). To gain mobility and speed, the spermatozoa likely utilize the relatively small diameter of the spermathecal duct to push themselves off the duct walls, rather than swimming freely in seminal fluid. The spermatozoa (approximately 1,250 microm) are considerably longer than the distance they have to travel along the spermathecal duct (approximately 800 microm). Our study provides the first direct observation of active sperm migration within the female of an insect stressing the importance of the genital tract as a prerequisite for functional sperm motility.