Life in a biological pool is so diverse that it is no surprise that butterflies live there underwater. Well, they are not butterflies capable of flying because they are just the butterfly larvae with the scientific name Parapoyns stratiotata that feed on leaves of aquatic plants as shown in the photo.

Those caterpillars are very active and live on aquatic plants underwater in tubular webs made of intertwined plant parts. Occasionally, they leave their web to fan themselves with oxygen-rich water, using oscillating movements of the front of their bodies. They feed on many different species of plants, always underwater.
The caterpillar can hibernate. To pupate, it weaves a dense, whitish cocoon. That one is filled with air and attached to the stem of host plant. Their flight period runs from May to September; in regions with favorable climatic conditions such as Portugal, at least two generations of butterflies are formed per year.

The presence of this species does not represent, in any way, a danger to aquatic vegetation. Having these larvae with us in the biological pool is an honor to host an insect whose biology is so adapted to aquatic life as a young animal and to the air as an adult.