Kleptoparasites

Kleptoparasites are animals that steal food or food-related resources that another animal has found, caught, stored, guarded, or prepared. This behavior is known as kleptoparasitism.¹ Although the term kleptoparasitism has ‘parasitism’ in it, its prefix comes from the Greek word kléptō, meaning ‘to steal.’² Unlike many parasites that usually feed on or inside the host’s body, a kleptoparasite usually steals a resource from the victim.

What distinguishes kleptoparasitism from other feeding behaviors is that, in this strategy, the kleptoparasite benefits at the expense of the animal that has acquired or prepared the food resource. The victim loses its food, time, energy, or even, in some cases, its reproductive investment.

Kleptoparasitism could be intraspecific, occurring between members of the same species, or interspecific, occurring between members of different species. For example, females of red-banded sand wasps may steal prey from nests made by other females of the same species.³ In contrast, frigatebirds harass other seabirds, such as boobies or terns, forcing them to drop or regurgitate food.⁴

How Kleptoparasites Work

Many kleptoparasites may actively seek chances to steal, whereas others steal opportunistically when another animal has already found, caught, or stored a valuable resource. Once the kleptoparasite senses the opportunity, it may chase, threaten, wait nearby, sneak in, or use deception to get access to the resource. If the attempt is successful, the victim may drop the food, regurgitate it, or abandon its resources for the kleptoparasite to take over.

Types and Examples

Since kleptoparasitism is a flexible feeding strategy, different animals have various ways of stealing food and resources.

• Chase-and-drop Theft: Some kleptoparasites, such as frigatebirds, skuas, jaegers, and gulls, harass or chase the victim until it drops, gives up, or regurgitates its food.
• Kill Takeover: Some animals, such as hyenas, wolves, coyotes, and jackals, displace another predator from prey it has already killed.
• Nest-provision Theft: Cuckoo bees, cuckoo wasps, some dung beetles, and Miltogrammine flies use food that another animal has stored or prepared for its own offspring.
• Deceptive Theft: Some birds, such as fork-tailed drongos, may produce false alarm calls or mimic the alarm calls of other species, causing animals to flee and abandon food.⁵
• Trapped or Captured Prey Theft: Some spiders of the genus Argyrodes, flies of the family Milichiidae,⁶ and flies of the genus Bengalia typically steal or feed on prey that another animal has already captured, trapped, or even partly eaten.⁷

Tradeoffs

To find, kill, or capture prey demands a high amount of energy for an animal. Instead of starting from scratch, it is easier for a kleptoparasite to take advantage of another animal that has already made all the effort.

However, stealing is not always an easy option. The victim may fiercely defend its prey and fight back in the attempt, which can injure the kleptoparasite or exhaust its energy. Moreover, if there are too many competitors aiming for the same resource, the effort needed to steal it may not be worthwhile.