Difference Between Lice and Crabs

Lice vs Crabs

Lice and crabs are completely different types of animals found among the invertebrates, yet these both belong to the same taxonomic phylum, Arthropoda, as they have jointed legs. Body size could be considered as the main external difference between them, but there are many other significant variations in lice from crabs. However, the common reference of some false crabs such as King crab, Hermit crab, Porcelain crab, Horseshoe crab, and Crab Lice could be confusing with the true crabs. Therefore, it would be importance to understand the actual characteristics of both lice and crabs together as in this article.


Lice are the insects that have been classified in the Order: Phthiraptera of the Superorder: Exopterygota. More than 3,000 lice species have been identified as of present. These wingless creatures can cause many problems for humans and other mammals being disease agents. However, they have not been a problem for the monotremes, but all other mammalian and avian species could be their hosts. In other words, lice have been defined as obligate ectoparasites of every mammal and bird.

Lice have a small head equipped with piercing and sucking mouthparts. Their thorax contains three pairs of legs in such a way that each leg has a claw with an opposing-thumb-like claw. Those claws are helpful for them to climb and move on hairy or feathery skins of mammals and birds. Females lay eggs after breeding, and the secreted saliva will keep the eggs attached to the hairs or feathers of the host. The lice eggs are commonly known as nits, and the nymphs are hatched from them. After going through three moults, nymphs become adults. Adult lice may be of different colours depending on the species and the amount of blood sucked. Their colours naturally range from pale beige to dark grey.

Some microbial diseases and helminthic infections can be transmitted into hosts from lice through their bites. In addition, heavy infestations can cause reductions in thermoregulation effects of plumage in birds. Furthermore, lice infestations could cause reduced life expectancy and sometimes to be defeated in sexual competitions.


Crabs are crustaceans with ten legs or with five pairs of legs so that they have been classified in the Order: Decapoda. There are more than 6,700 species of crabs in the world, out of which the vast majority is found in the sea, and only about 850 species live in the freshwater or terrestrial environments. Although it was believed that the modern crabs have been originated from a single precursor, the evolutionary evidences suggest two lineages from distinct ancestors to have new world and old world types. However, the main feature of crabs is their large carapace that covers them, but the tail is hidden ventrally underneath the body. This large carapace is made up of calcium, and it provides a great deal of protection for the crab in many ways such as being an exoskeleton and a surface for muscle attachment.

Sexual dimorphism is prominent in crabs, though it is not readily seen to the exterior, which is because their tails (abdomens) exhibit the main difference between males and females. Abdomen is broad and round in females, whereas males have a narrow and triangular shaped abdomen. The most interesting behaviour of crabs is that they move sideways but not forward and backward. However, there are few species with the capability to walk forward and backward, as well. Crabs are well known as delicious food around the world, which means they are a great protein resource for the humankind.

Lice vs Crabs

• Both are arthropods, but crabs and lice have been classified in different taxonomic classes.

• Lice have three pairs of legs, whereas crabs have five pairs of legs.

• Lice are always parasites of other animals, but crabs are not being parasitic very often.

• Lice are nuisance for humans, but crabs are a delicious resource of protein for humans.

• Crabs have an external carapace but not the lice.

• Crabs are much larger than lice in their body sizes.

• Lice can move forward and backwards, whereas crabs can walk only sideways.