Armadillidiidae

Pill bugs in the family Armadillidiidae are able to form their bodies into a ball shape, in a process known as conglobation. Conglobation has evolved independently in several families; this behaviour is shared with pill millipedes (which are often confused with pill bugs), armadillos, cuckoo wasps, and some extinct trilobites. It may be triggered by stimuli such as vibrations or pressure, and is a key defense against predation; it may also reduce respiratory water losses. This defense mechanism is possible because of their segmented body structure. Armadillidiidae have overlapping plates called tergites that are connected by flexible joints. The tergites allow the body to roll up inwards. To roll up, they have muscles called pleopods that contract the abdominal tergites inwards.

The diet of pill bugs is largely made up of decaying or decomposed plant matter such as leaves and, to a lesser extent, wood fibers. Pill bugs also eat living plants, especially in wet conditions, sometimes consuming leaves, stems, shoots, roots, tubers, and fruits. Some species of pill bugs are known to eat decaying animal flesh or feces. They will also eat shed snakeskin and dead bugs, if necessary. This diet has a secondary effect of accelerating the breakdown of litter, aiding in the retention of organic material in the soil. This helps in balancing the carbon content in the soil. Pill bugs also contribute to their ecosystem as detritivores.

Pill bugs are often found in damp places with ample amounts of decaying matter, such as leaf litter and compost piles. However, pill bugs can be serious pests in certain agricultural systems, particularly in areas that are prone to heavy rains and flood conditions.

Pill bugs will feed on numerous crop plants including corn, beans, squash, peas, melon, chard, beet, cucumber, potato, spinach, lettuce, and strawberry, with potential for significant yield loss in strawberry in particular. Since they are attracted to decaying plant matter, they are often found on farms eating the crop residue, which can lead them to start eating emerging seedlings. This has started to pose agricultural problems in Southern Australia. Farmers in the United States and Argentina have also reported increased rates of pill bugs destroying seed oil and soybean crops. They have also been observed eating wood supports in houses, making them a house pest.

The family Armadillidiidae is differentiated from other woodlouse families by the two-segmented nature of the antennal flagellum, by the form of the uropods, and by the ability to roll into a ball.

Within the family Armadillidiidae, 18 genera are currently recognized:==August 2026==

Seventeen of these are:

• Alloschizidium Verhoeff, 1919 (13 species)
• Armadillidium Brandt, 1831 (more than 200 species)
• Ballodillium Vandel, 1961 (monotypic)
• Cristarmadillidium Arcangeli, 1936 (4 species)
• Cyphodillidium Verhoeff, 1939 (monotypic)
• Echinarmadillidium Verhoeff, 1901 (3 species)
• Eleoniscus Racovitza, 1907 (monotypic)
• Eluma Budde-Lund, 1885 (5 species)
• Estenarmadillidium Cifuentes, 2021 (monotypic)
• Paraschizidium Verhoeff, 1919 (5 species)
• Paxodillidium Schmalfuss, 1985 (monotypic)
• Platanosphaera Strouhal, 1956 (6 species)
• Schizidium Verhoeff, 1901 (26 species)
• Trichodillidium Schmalfuss, 1989 (3 species)
• Troglarmadillidium Verhoeff, 1900 (8 species)
• Trogleluma Vandel, 1946 (2 species)
• Typhlarmadillidium Verhoeff, 1900 (4 species)

A 2022 study of myrmecophilous populations indicated that these represented a new species of Cristarmadillidium, and three new species within a new genus, Iberiarmadillidium.