Predation occurs when one animal eats other animals and kills them. The animal that is killed is called the prey and the animal that does the killing is called the predator.

Symbiosis means living together, and there are three kinds of symbiotic relationships between species:

• Parasitism. Where the parasite receives some benefit from the host and by doing so harms the host.
• Commensalism. Where one partner receives some benefit from the other without harming or benefiting the other partner.
• Mutualism. Where both partners benefit from the relationship.

Predators

Probably more bumblebees are killed by parasites (see right) than by predators. This may be because the bumblebee females are armed with a sting, but it is also due to the protection given by their warning colouration.

Some crab spiders ambush bumblebees at flowers. These spiders do not spin webs, but sit and wait for their prey to come within reach. They are well camouflaged. In north America Misumenia vatia catches bumblebees as they land on flowers.

Robber flies catch their prey on the wing in their legs. And in the U. S. A. have been found to prey on bumblebees.

A few species of bird can remove the sting before eating the bumblebee, e.g. bee-eaters, spotted flycatchers and shrikes.

In the U. S. there are wasps called beewolves in the genus Philanthus, these wasps specialise in hunting bumblebees. The bumblebee is caught while feeding and is paralysed with a sting, it is taken back to the nest and enclosed with a wasp egg in a cell, there are usually about five bumblebees in each cell.

Predation of foraging bumblebees -almost the only time when humans see them is relatively rare. All of the above are predators of foraging bumblebees.

Other predators break into nests and include badgers, who will eat the entire brood, wax, stored food and any adult bees that do not escape. In north America skunks do the same. Foxes, minks, weasels, bears, field mice and shrews are also predators. In Iceland the mink is the major predator. However there is no mammal that specialises in bumblebee predation.

Parasites

Cuckoo bumblebees, Psithyrus spp. Cuckoo females enter the bumblebee nest and lay their eggs, the bumblebee workers then rear these eggs as if they were their own sisters and brothers. These bumblebees have no pollen baskets on their rearmost legs, and do not secrete wax for nest construction. There is no worker caste, and all cuckoo bumblebee eggs hatch as reproductive males or females.

Wax moth, Aphomia sociella. In northern Europe the wax moth is regarded as the most serious enemy of the bumblebee, and is found only in bumblebee nests. In some areas in southern England as many as 80% of nests can be destroyed. The adult moth flies from June - August. It enters the bumblebee nest and lays her eggs, at first the caterpillars feed on nest debris, but as they grow they switch to feeding on the wax food cells, food stores and even larvae. Normally this destroys the nest. The moth leaves the nest to overwinter as a pupa in a sheltered spot, It spins a strong, brown cocoon in autumn. In the UK bumblebee boxes have become popular in recent years. If your box is invaded by the wax moth than I'm afraid there is little you can do for the nest as by the time you have discovered it it is too late. All you can do is clear out the nest contents and get it ready for the next year. Invasion of the nest by the north American wax moth Vitula edmandsii does not always lead to the destruction of the nest as it does not feed on the larvae.

Brachicoma devia in Europe and Barchicoma sarcophagina in north America is a fly that look a little like the common house fly. The female enters the bumblebee nest and lays larvae (this fly does not lay eggs) among the bumblebee larvae. The fly larvae attach themselves to a bumblebee larvae and wait. Once the bumblebee larva has spun its cocoon the fly larvae start feeding on it and suck it dry. When they are fully grown they (one bumblebee cocoon can support 4 parasitic larvae) leave the bumblebee cocoon and pupate in the bumblebee nest. A heavy infestation will lead to the death of a colony.

Conopid flies. The female fly waits on flowers till a bumblebee comes to feed, then she jumps on the bee and quickly pierces the bee's body laying her egg inside. The egg hatches inside the bee and feeds off its abdominal contents till it more or less fills the entire abdomen. The bumblebee dies after about 10 days and the fly larva pupates inside the husk of the dead bumblebee body emerging as an adult fly next summer. This parasite can change the behaviour of the bumblebee. Infected workers tend to stay outside the nest more than other workers, often remaining out all night, and they tend to favour colder microclimates, also before the bumblebee dies it attempts to bury itself. In Europe bumblebee queens are not usually parasitised as they emerge before the adult fly emerges. In the U. K. Conopids are usually active from June - August.

Mites. Locustacarus buchneri lives in the air sacs of the bee where it feeds on the haemolymph. It will not kill a colony, but it will weaken one. The mites hibernate inside new queens.

Parasitic wasps. These small wasps lay numbers of eggs inside the adult bumblebee and the wasp larvae eat the bumblebee from the inside.