American spider beetle

American spider beetle
American spider beetle
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Anobiidae
Genus: Mezium
Species: Mezium americanum
Binomial name
M. americanum

The American Spider Beetle is a scavenger found in various locations around the world. It is generally seen as a pest that needs to be exterminated as they can be found feasting on a large variety of foodstuffs wherever they are stored. Often mistaken for being part of the order Araneae for its spider-like appearance, it is actually part of the order Coleoptera. This beetle is notable for its survival in extreme conditions like desiccation and freezing temperatures.



The American spider beetle (Mezium americanum) is about 3 mm in length. Its body is dull yellow, with a glossy black elytra. The beetle has blunt projections on each side of an almost cylindrical thorax.[1] The prothorax is constricted at the base of the elytra.[2] It tends to be pear-shaped and convex, with its elytra appearing swollen, giving the impression of a glass bead with legs. The antennae and legs are long and slender, which give it a spider-like appearance, and these tend to be pale brown to yellow.[1] The antennae are filamentous, and arise on the front of the head where they are close together at their base. The segmented abdomen is covered in long hairs. Larva are grub-like, with short legs and cream-coloured bodies.[2]

Natural history


Mezium americanum is a cosmopolitan species, but is an exotic species in Australia.[3]

Life cycle

Like other beetles, the American spider beetle has holometabolous development. The beetles usually appear in the spring. The female will lay approximately 40 eggs on or in proximity to a food source, often grain. The eggs are spindle-shaped and very small. Eggs hatch into larvae which reach about 1/8 of an inch in length. Development takes about 3 months with 3 molts before a pupal phase. The larva can over-winter in this pupal cell with pupation occurring the following spring.[2] There may be one to two generations per year, depending on the ambient temperature and humidity.


Food is often grain, but the spider beetle also eats dried vegetable or animal matter, and even wools and textiles. All types of grain and grain-products are consumed as well as nuts, animal skins, beans, paper and wood, cacao and chocloate, dead insects and other animals, dried fruit and vegetable matter, excement, feathers and hair, and some living plants.[4] It also has a taste for the exotic, dining on such items as cayenne pepper, tobacco and opium.[1] These plants contain chemicals which would be toxic to many other species.

Behaviour and adaptations

Unlike most beetles, spider beetles cannot fly because their wing-coverings (elytra) have fused to create a solid, hard shell. This one-piece suit prevents the insect from losing water – an important trait for living in dry environments.

The beetle is able to survive without drinking water for over seven years. Spiracles that open internally aid in this incredible feat. This moisture-retaining adaptation is usually restricted to desert species, but the spider beetle uses it to live in extremely dry stored grain. The beetle can also reclaim water from its own urine. It is truly an efficient water-user. Even food is a luxury the spider beetle can do without. When food is scarce, an adult can enter quiescence – a period of inactivity where it hardly moves and would appear dead to the unknowing observer. When conditions improve, the beetle comes out of its “suspended animation” to feast.

The American spider beetle is certainly a marvel of nature – a living testament to the power of evolution to create creatures that will survive under the harshest of conditions.[5] The beetles typically forage at night and thus are rarely seen. They can be active in temperatures below freezing.[4]

Human Impacts

Common infestation sites in a house can also be wall voids and drop ceilings. Hence, this beetle can not only damage certain food products but also can damage the house.[6] As a pest species, this beetle is subject to extermination whenever an infestation is found. A few methods of extermination includes heating the infested product to a high temperature, placing it into a deep freezing temperature, microwaves or the use of insecticides that use a chemical compound called a pyrethroid.[7] In addition, thoroughly clean storage facilities beforehand by use of a strong suction vacuum cleaner to eliminate favorable development places. Inspect stored foods routinely and eliminate any dampness or high humidity conditions. Eliminate rodents, birds, and other insects as spider beetles feed on feces and dead insects.[6]


  1. ^ a b c Milne, L. and M. Milne. 1980. The Audubon Society Field Guide to North American Insects and Spiders. 8th printing. Alfred A. Knopf Inc, New York, N.Y.
  2. ^ a b c
  3. ^
  4. ^ a b
  5. ^ Benoit J. B., J.A. Yoder, E. J. Rellinger, J. T. Ark, and G. D. Keeney. 2005. Prolonged maintenance of water balance by adult females of the American spider beetle, Mezium affine Boieldieu, in the absence of food and water resources. Journal of Insect Physiology, 51, 565-573.
  6. ^ a b
  7. ^

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