Crustaceans – a December reminder of the role of these aquatic insects


On December 11, we celebrate Crunch Day. It draws attention to these often underestimated but extremely important aquatic insects. Crustaceans, a key component of the food chain in freshwater ecosystems, also act as bioindicators, helping to monitor the health of our waters. In the face of threats such as pollution, climate change and habitat loss, Hogweed Day is a reminder of the need to protect these precious creatures, but also the entire ecosystems in which they live and which they support.

Crisscross Day

Crisscross Day was put on the calendar in 2002. There is an interesting anecdote related to this. That’s when Lech Pietrzak, a doctoral student from the Department of Ecology and Environmental Protection at the University of Warmia and Mazury in Olsztyn, heard a radio program dedicated to unusual holidays during his research on caddisflies. He learned from it that December 11 has no holiday assigned and a competition was announced to propose a patron saint for the day. He proposed celebrating the Day of the Crisscross.

His idea was well received by the audience, which led to the establishment of this holiday. The first official celebration took place in 2003. In Olsztyn, on Lake Kortowski. Since then, the day has been celebrated annually with scientific seminars and popular science sessions. These meetings bring together both caddisfly researchers and enthusiasts of other aquatic insects from all over Poland.

Let’s get to know these little insects better

Crustaceans (Trichoptera) are insects that resemble butterflies, with which they are closely related. About 10,000 have been identified worldwide. species, including more than 900 in Europe and about 270 in Poland. Most caddisfly larvae live in freshwater bodies, although some are also found on land, such as in layers of moss and rotting mulch. These insects are small in size, from 2 mm to 4-5 cm. Crustaceans differ from butterflies in the absence of suckers and scales on their wings – instead they have chitinous hairs. They are inconspicuously colored insects, usually gray, black or brown, sometimes with red or yellow accents. Their feelers are long, often longer than their entire body.

Crustaceans are mainly active at night and dusk, during the day they hide near bodies of water. They are weak fliers and feed on the nectar of flowers. Female caddisflies lay their eggs directly into the water or on the leaves of above-water plants. Egg development takes 2 to 4 weeks, and adults live on land for only about 8 days. The most important moment in their lives is the mating flight, which for most native species falls between early June and late August.

The caddisfly larvae are divided into two groups: caterpillar larvae, which live in houses, and campodeal larvae, which rarely build them. The caterpillar larvae’s homes are made of a variety of natural materials, such as reed pieces, leaf fragments, spruce needles, seeds, shells, , sand and small pebbles. These houses protect the larva’s soft body and are expanded as it grows. These animals feed on plants, algae and detritus. Campodeal larvae, which live in flowing waters or lakes with strong ripples, often have a predatory lifestyle. They hunt small aquatic organisms using reticulated perches – hunting nets.

The caddisfly larvae, after a period of growth, prepare for pupation by building a pupal cocoon. After 2-3 weeks, they transform into the adult form. Most have a one-year life cycle, although some may have a longer cycle or produce two generations per year.

Crustaceans - a December reminder of the role of these aquatic insects 1

Crustaceans and their role in the food chain

Crustaceans play a key role in aquatic ecosystems, serving as both consumers and food sources for other organisms:

  • Recycling organic matter: caddisfly larvae feed on detritus, or dead organic matter, meaning dead plant and animal fragments. By doing so, they contribute to keeping the waters clean by preventing excessive accumulation of organic waste. Crustaceans help recycle nutrients, which is crucial to the health of aquatic ecosystems;
  • food source in the food chain: caddisfly larvae are an important food source for many species of fish and other aquatic animals, thanks to their nutritional value and abundant occurrence;
  • Food for birds and bats: adult caddisflies, due to their poor flight capabilities, often fall prey to birds, bats and other insects.

Crustaceans as indicators of water quality

Crustaceans are also known as bioindicators, meaning that their presence or absence can provide valuable information about the state of the aquatic environment. Some species are particularly sensitive to pollution, so their abundance or lack of occurrence can indicate water quality. Monitoring caddisfly populations is therefore an important tool in assessing the health of aquatic ecosystems.

What threatens them?

The caddisfly population is exposed to many threats. Water pollution, eutrophication, climate change, invasive species, habitat loss and excessive urbanization are just a few. Understanding these dangers and taking action to protect aquatic habitats is key to preserving these valuable insects. By raising public awareness and engaging in conservation and educational activities, we can help protect these small but vitally important creatures. We must remember that the health of the waters is directly linked to the health of the entire environment, and thus the health of people.

Did you know that.

  • The oldest crinoid fossils date back to the Permian;
  • Until the mid-20th century. Their name was recorded as “chrósts.”
  • in different regions of Poland have local names, such as padlocks, klajduki or hems.

Source: Wikipedia/Bruce Marlin, CC BY-SA 2.5 ,

Używamy plików cookie, aby zapewnić najlepszą jakość korzystania z Internetu. Zgadzając się, zgadzasz się na użycie plików cookie zgodnie z naszą polityką plików cookie.

Close Popup
Privacy Settings saved!
Ustawienie prywatności

Kiedy odwiedzasz dowolną witrynę internetową, może ona przechowywać lub pobierać informacje w Twojej przeglądarce, głównie w formie plików cookie. Tutaj możesz kontrolować swoje osobiste usługi cookie.

These cookies are necessary for the website to function and cannot be switched off in our systems.

Technical Cookies
In order to use this website we use the following technically required cookies
  • wordpress_test_cookie
  • wordpress_logged_in_
  • wordpress_sec

For perfomance reasons we use Cloudflare as a CDN network. This saves a cookie "__cfduid" to apply security settings on a per-client basis. This cookie is strictly necessary for Cloudflare's security features and cannot be turned off.
  • __cfduid