Cuticular evidence of traumatic experiences of water beetles (Coleoptera :Dytiscidae, Hydrophilidae)

Scratch marks of various forms were observed on the cuticle of larger aquat ic beetles. The distribution of multiple scratches (MS), those that occur a s groupings of deep parallel lines, was recorded from a sample of 1,233 bee tles of the Austrodytes Watts, Cybister Curtis, Dytiscus L., Homocodytes Re gimbart, Hydaticus ils Leach (Dytiscidae) and Hydrophilus Muller (Hydrophil idne) from a variety of geographical areas. The number of scratches differe d significantly between taxa, being highest in Austrodytes, Cybister and Ho moeodytes. Also, beetles from tropical areas had a higher incidence of MS t han beetles from north temperate and subarctic regions. The number of MS di d not differ between sexes but increased with age of the beetle. They do no t appear to be caused by collection or handling of the specimens. It is pos tulated that MS are produced by predator attacks and are most prevalent amo ngst large beetles that occur in relatively open habitats in tropical areas . The predator involved is not known bur the nature of the MS and the habit at and geographical distribution of beetles bearing MS makes snakes the mos t likely candidate. Taxa with the greatest frequency of MS also had the thi ckest cuticle suggesting that predation pressure may be a factor selecting for thick, hard to grasp cuticle.