Flightless beetles on islands: distribution and life history of darkling beetles of the genus Branchus (Coleoptera: Tenebrionidae)

Darkling beetles of the genus Branchus LeConte are all flightless, each of the known species being restricted to localized, semi-arid areas from Panama to southern Texas, and eastward through the Greater Antilles and southern Florida, to the Turks and Caicos Islands, with species unique to each island or bank of islands. The secretive beetles and larvae live on and in loose sandy soils under plant debris in dry forest habitats. Antillean and Bahamian specimens have been collected under leaf litter, palm thatch and wood debris on high sandy ground behind the beach strand, in sites partly shaded by shrub or small tree canopy, e.g. Bursera, Coccothrinax, Coccoloba on deep, coarse, coral sand, often at edges of light gaps in dry sites but under larger accumulations of palm thatch and leaf litter. Beetles are usually exposed at the sand surface but nestled in small depressions or sometimes immediately under the sand surface. Associated larvae occur deeper in the sand, usually 2-6 cm, and are often found in greater numbers than adults. The sand-burrowing larvae are slender, pale, cylindrical, up to 4 cm in length, with dark shovel-like mandibles, large forelegs modified for digging, and characteristic “crown” of spines on the abdominal apex (9th tergum). Pupation takes place in semi-moist sand in an elliptical cell prepared by the larva; adults emerge within 2 weeks, and are probably long-lived. Survival of Branchus populations is threatened by habitat loss due to coastal development and the spread of introduced Casuarina trees which shade out and replace native vegetation. Branchus specimens are rare in most museum collections. The majority of known species in collections are represented by single or very few specimens, and many remain to be described.