What Do Spider Beetle Adults and Larvae Look Like?

What Do Adult Spider Beetles Look Like?

Adults are tiny, only 2–3 mm long, with an oval body that's reddish-brown to dark brown and glossy. The most noticeable feature is their very long, slender legs, which make them look somewhat like spiders. The elytra (wing covers) are smooth and hairless, covering the entire abdomen. When startled, they play dead — tucking their legs in and staying completely still, looking like a tiny seed.

What Do Spider Beetle Larvae Look Like?

The larvae look completely different from the adults — they're typical scarabaeiform (grub-type) larvae:

• Body is C-shaped, like a tiny crescent moon
• Creamy white or pale yellow, body is soft
• Three pairs of short thoracic legs
• Body has fine bristles (setae)
• Head is darker than the body — pale brown

Larval Life Habits

• Larvae have weak mobility and don't crawl around much
• They stay right where the adult laid eggs — in the grain pile or food crumbs
• They eat, defecate, and grow all in the same food pile
• The larval stage lasts about 4–8 weeks; they molt several times before pupating
• They build a cocoon chamber in the food debris to pupate

How to Find Them

Because adults are only 2–3 mm and larvae hide inside food piles, they're hard to spot during routine checks. When inspecting, pour the grain out onto white paper and examine carefully, or sift it with a sieve to look for tiny insects and powder.