Natural History Photographs

Feeding on waste products

Butterflies are highly specialized feeders. Their proboscis ('tongue') is their feeding organ, whichs can only be used to suck fluids. We are quite used to butterflies sucking nectar from flowers. However, though the butterfly gains copious amounts of moisture and sugars this way, other nutritious stuff like amino acids are almost absent from nectar. They have to accumulate other nutrition during the larval stage.

Although this holds true for many butterflies, it certainly does not for all of them. Some butterflies are hardly ever seen on flowers, for example the Purple Emperor. It has a quite different proboscis, as you might notice: it's yellow instead of the normal black. I have seen them feeding on manure and other faecal material. They probably get nitrogen this way, highly important for making protein. This way they might prolong their life span. Another way to get nitrogen is to feed on carrion, as can be seen in Erebia pronoe below. The Dark-green Fritillary below feeds on some animal waste product.

Argynnis aglaja
Feeding on ill-defined animal waste.

Erebia pronoe
Feeding on a dead shrew.

A rather unexpected food source for butterflies (to me at least) is rotting plant material. The most nutricious parts of plants (highest protein content) are flowers and seeds. Normally this food source is unavailable to butterflies, due to their highly specialized proboscis. However, the photograph below show how a butterfly capitalizes on the plant's failure to reproduce. The rotting of the bud makes the nutritious stuff available to this opportunist.

Polygonia c-abum - the Comma, feeding on rotting
flower bud of Woolly Thistle, Cirsium eriophorum
Sometimes it is even unsure what a butterfly is eating. Both butterflies shown below were feeding on the unopened flowerhead of some thistle. Though leafs cover the flowerhead visited by Kirinia, suggesting that the flowerhead is affected by some insect larvae, the flowerhead visited by Brintesia seems perfectly normal. I thus have no clue as to the food source these butterflies are after...
Brintesia circe
Kirinia roxelana

Even though most butterflies use flowers as a source of sugars, there are more options even here. Aphids live from plant juices, which are rich in sugar but poor in nitrogen. As a result, the aphids have to consume much more juice than necessary from an energetic point of view. The surplus sugars spill from the aphids body onto the plant. If you ever parked your car below an aphid-laden tree, you may have notices a sweet sticky substance on your car; this is called honeydew, and it is produced by the aphids. Sometimes butterflies use this as an alternative food source, as you can see here.

Celastrina argiolus feeding on honeydew.
Polygonia c-album feeding on honeydew.
(Short film fragment, 5 Mb).