The relationship between body form and habit in some Carabidae (Coleoptera)
Authors: FORSYTHE TREVOR G. 
Published: March 2009

Variations in height of prothorax and hind body; hind body, prothorax, labrum, clypeus and metatergum widths; metasternum, metatergum and wing lengths; eye protuberance and width of antennal insertions are discussed and compared with body lengths in different species of carabid beetles. These various parameters have been displayed in the form of tables, ratios and graphs; they have also been discussed in relation to the various habits (i.e. feeding, locomotory, burrowing, flying) of the different carabid beetles; certain trends were noted.

The Carabini were found to be generally heavier and greater in volume (i.e. bulkier) than other carabid beetles, and this is reflected mainly in the size of the hind body, notably hind body depth. The Carabini are also much stronger than other Carabinae group I species. The explanation for this probably lies in the nature of the leg muscles and their coxal insertions. This is reflected in the prothorax which is significantly deeper and may reflect the size of the contained extrinsic procoxal muscles. It was suggested that the size, bulk and strength of the Carabini may help them overcome the ‘environmental resistance’ of their various habitats.

Ground beetles which live in restricting or confining habitats, such as in fissures in the ground, have a tendency to be narrower in width and shallower in depth, with a prothorax similar in width to the hind body. It was suggested that this type of body form would minimize friction by causing less obstruction when moving through confined spaces.

Visually hunting carabid beetles (spp. of Cicindela, Elaphrus, Notiophilus and Asaphidion) have large eyes which protrude significantly more than those of species which hunt using other senses (i.e. tactile and olfactory). The prothorax of these species (apart from Notiophilus) is also significantly narrower than the hind body. It was suggested that the combination of these two features increases the area of the visual field and enhances their hunting abilities. Additionally, a narrow prothorax may allow the elytra to open quickly, and swing forwards without hinder‐ance from prothoracic margins; this is essential in a beetle that hunts in the open where the ability to escape rapidly by flying greatly reduces the possibility of predation. In Notiophilus, however, the prothorax is similar in width to that of the majority of other ground beetles. This structural difference is probably correlated with its special feeding habits, its particular hunting strategy and its habitats.

In Cicindela, the feeding apparatus is modified to form a unique fluid‐feeding mechanism. Considerable secondary morphological changes have modified the head structure. In particular, the labrum and clypeus have expanded laterally and the positions of the eyes and antennal insertions have shifted dorsally.

In some ground beetles, atrophy of the wings and their associated muscles has resulted in changes to the meso‐ and metathorax. This is reflected in a decrease in the sizes of the metatergum and met‐episternum, and a rounding of the elytral humeri. The metasternum is also smaller, and this effectively alters the positions of the meso‐ and metacoxae. Although the body form of constantly brachypterous ground beetles has undergone these morphological changes, there has been no noticeable effect on their running and pushing abilities.