P. callosus is a polyphagous (feeding on different food) pest. It has been reported feeding on a wide range of monocotyledonous and dicotyledonous species, including grasses, herbs and woody plants. It has not been recorded feeding or damaging gymnosperms.
The adult P. callosus attacks leaves, green stems and fruit while the larvae have an impact on a wider range of species where damage results from them feeding on roots or tubers below ground.
Phlyctinus callosus adults are 7 mm long, dull grayish-brown with a much lighter or white V-shaped band at the rear of the abdomen on the closed elytra. The tip of the rostrum is black and shiny. The abdomen is bulbous. To the posterior of the abdomen, beyond the white V-shaped band, the elytra are distinctly 'lumpy'. Each lump bears numerous setae (bristle).
The eggs are oblong, about 0.9 mm long and creamy white when first laid, but turning black at each end as they age.
Larvae are creamy white, legless and up to 6 mm long, with long hairs on the body. They have orange head capsules and black jaws. There are four to 11 larval instars, although most larvae have six to nine instars. The pupae are 7-8 mm long and have stout, hooked bristles.