Family Phengodidae - Glowworm Beetles

Glow-worms, Railroad Worms

the Asian Rhagophthalmidae (~30 spp.) formerly included here as subfamily are now treated as a separate familyl(1)

Phengodidae LeConte 1861

23 spp. in 6 genera of 2 tribes north of Mexico, ~250 spp. in ~30 genera total(2)

Adult males have variously shortened/narrowed soft elytra, branched antennae, and bulging eyes; adult females are larviform (often all but impossible to tell from fully-grown larvae) and, like the larvae, have bioluminescent organs(2)

Adult females larviform, differing only slightly in external appearance from mature larvae in absence of larval setae from sterna and terga of abdominal segments 9 and 10, presence of gonopore beneath large, transverse fold on abdominal segment 10, and presence of compound eyes (2).

Also, per J.M. Cicero: "Adult females are much larger, having supernumerated beyond the male instar count and/or grown larger on nutritional bases; we don't know which of these factors is responsible for the larger size. Zarhipis and Phengodes larvae, at least, have strong opaque dorsal sclerites while in the female, those markings are bleached and weak. Lastly, females have a semi-circular slit on the penultimate ventrite that is associated with a copulatory gonopore. Larvae don't have either."

New World; in our area, mostly so. US, with 1 sp. (Phengodes plumosa) reaching ON and all Mastinocerini restricted to sw. US (CA-TX)(2)(3)

adult females and larvae feed on millipedes(2); adult males do not feed

Larvae run alongside millipedes, then stop it by curling themselves around the front of their body. The larvae then bites the millipede behind and underneath the head, paralyzing it with toxins and digestive enzymes. Immobilized, the millipede doesn't release their noxious defensive chemicals and quickly dies. The larvae consumes everything but the exoskeleton and defensive glands.(4)

mostly nocturnal; males come to lights; females much more commonly encountered than larvae(5)