Year 1 day 0Water 0 °CNymphs 0 /m²Adults 0 /m²Mosquito larvae 0 /m²FPS 0

Drag to orbit, wheel or pinch to zoom. Animals are drawn about 10 times too large and their numbers are scaled from the density per m². Brown nymphs live on the pond floor and reed stems; pale husks on the reeds are shed nymph skins (exuviae) from this year's emergence; thin larvae hang from the water surface.

Dragonfly Wetland Nymph Lab

A dragonfly spends most of its life underwater as a nymph. Grow the pond's population through six years of degree-days, reeds and fish, and see how many mosquito larvae the nymphs eat.

Habitat

Climate

Time

Live readouts

Nymphs per m² by size class

Water temperature (°C) and development threshold

Mosquito larvae per m²

Experiments

Each runs all six years headless for several values and reports the last year.

Independent numerical checks

Controls and missions

Drag / one finger: orbit; wheel / pinch: zoom. The day slider scrubs through the six simulated years (it pauses playback).
Mission 1: find the smallest reed density that keeps the population alive with the default fish pressure.
Mission 2: how much do nymphs reduce mosquito larvae in the last year, compared with a pond without dragonflies?
Mission 3: warm the pond by 3 K and compare the years from egg to emergence.
Mission 4: turn the fish pressure up and then add reeds; can reed refuge compensate?

The science

Development by degree-days. Cold-blooded animals develop in proportion to accumulated heat above a threshold: dD/dt = max(0, T_w − T₀) with T₀ = 8 °C. Eggs hatch after 140 degree-days; a nymph passes 10 instars and is ready to emerge at about 1,500 degree-days. Pond temperature is T_w = T_m + warming + A cos(2π(d − 205)/365); its yearly degree-days have a closed form that the checks below compare with the daily sum.

Food and growth. A nymph eats mosquito larvae with a Holling type II functional response f = aM/(1 + a h M) (a grows with body size, handling time h = 1/6 day), and 80 % of its needs are met by other prey. Growth speed is scaled by the fraction of its daily need that is met.

Mortality. Per-day loss μ = μ₀ + μ_fish/(1 + reeds/60) + μ_can N/K_n: background, fish predation reduced by refuge among reed stems, and cannibalism (K_n rises with reeds). Mature nymphs climb reed stems to emerge between days 110 and 250 when the water is at least 11 °C; success is reeds/(reeds + 25) because no perch means no emergence.

Adults and eggs. Adults live about two weeks (daily survival 0.93), mature in 10 days and lay eggs in reed stems when the air is at least 15 °C: eggs scale with reeds/(reeds + 40). Mosquito larvae grow logistically, dM/dt = r(T) M (1 − M/K) + immigration − nymph feeding, K = 3,000 per m²; the dashed baseline shows the same pond without dragonflies.

Simplifications and honesty. One generic dragonfly species is modelled with parameters that are typical or tuned for a plausible pond (nymph densities of 10 to 100 per m²); the real values vary widely between species, many of which need two to five years. Cohorts are not individual animals, there is no wetland hydrology, drying, winter ice, pollution, birds or competing predators, mosquito adults are not modelled, and the strong effects of reeds and fish are partly built into the chosen coefficients. The numbers show how the mechanisms interact, not a forecast for any real pond. Animals are drawn about 10 times too large. Assets were modelled in Blender; the animals, flight and numbers are driven by the simulation on this page.