Kleptoparasitism or cleptoparasitism (literally, parasitism by theft) is a form of feeding where one animal takes prey from another that has caught, killed, or otherwise prepared, including stored food (as in the case of cuckoo bees, which lay their eggs on the pollen masses made by other bees). Kleptoparasitism is also the 'stealing' nest material or other inanimate objects from one animal by another.
The kleptoparasite gains either by obtaining prey or other objects that it could not obtain itself, or by saving the time and effort required to obtain it. However, the kleptoparasite may run the risk of injury from the victim if it is able to defend its property.
Kleptoparasitism may be intraspecific, where the parasite is the same species as the victim, or interspecific, where the parasite is a different species. In the latter case, the parasites are commonly close relatives of the organisms they parasitize ("Emery's Rule").
Animals that have extraordinarily specialized feeding methods are often targets of kleptoparasitism. For example, oystercatchers are unusual in being able to break through the shells of mussels; adult oystercatchers suffer intraspecific kleptoparasitism from juveniles that are not yet strong or skillful enough to open mussels easily. Diving birds that bring their prey to the surface suffer interspecific kleptoparasitism from gulls, which are unable to fetch fish from the sea floor themselves.

Arthropods
There are many different lineages of cuckoo bees, all of which lay their eggs in the nest cells of other bees, and a family of cuckoo wasps also exists, many of which lay their eggs in the nests of potter and mud dauber wasps; many other lineages of wasps in various families have evolved similar habits. These insects are normally referred to as "cleptoparasites," rather than as "brood parasites." The distinction is that the term "brood parasite" is generally restricted to cases where the immature parasite is fed directly by the adult of the host, and raised as the host's offspring (as is common in birds). Such cases are virtually unknown in bees and wasps, which tend to provide all of the food for the larva before the egg is laid; in only a few exceptional cases (such as parasitic bumblebees) will a bee or wasp female actively feed a larva that is not her own species. The difference is only in the nature of the interaction by which the transfer of resources occurs (tricking a host into handing over food rather than stealing it by force or stealth), which is why brood parasitism is considered a special form of kleptoparasitism.

Bees and wasps
Some flies are kleptoparasites. This includes several flies of the Chloropidae and Milichiidae families. Some adult milichiids, for example, visit spider webs where they scavenge on half-eaten stink bugs. Others are associated with robber flies (Asilidae). Flies in the genus Bengalia (Calliphoridae) steal food and pupae transported by ants and are often found beside their foraging trails.

Flies
Kleptoparasitic spiders, which steal or feed on prey captured by other spiders, are known to occur in five families:

Theridiidae (Argyrodes species)
Dictynidae (Archaeodictyna ulova)
Salticidae (species of Portia and Simaetha)
Symphytognathidae (Curimagua bayano)
Mysmenidae (Isela okuncana, Kilifia inquilina, and Mysmenopsis species). Spiders
Many semiaquatic bugs (Heteroptera) are known to engage in kleptoparastism of prey. In one study, whenever the bug Velia caprai (Water Cricket) took prey heaver than 7.9 g, other bugs of the same species joined it and successfully ate parts of the prey.

Birds
The relationship between Spotted Hyenas and Lions, in which each species steals the other's kills,
The Cheetah has killed an Impala and eaten part. It is now digesting.
Three minutes later: this Spotted Hyena and another are running toward the kill.
38 seconds later: The Cheetah has fled without resistance. The vultures will also engage in kleptoparasitism: When the hyenas move a piece of the carcass, the vultures will take scraps from the ground.