Just what are the chances of butterfly eggs reaching adulthood? Richard Jones takes a look at the evidence
Standard population dynamics would suggest that, on average, two eggs from each female need to
survive. Thus two parents from one generation are succeeded by two offspring in the next (though
this may be complicated by males mating with multiple females).
Being unprotected and immobile, eggs are easy prey, so most butterflies lay them singly, widely scattered on the foodplants. Often the first act of the hatchling caterpillar is to eat its own eggshell, so cannibalism is a possibility too.
Some, like the small skipper leave small clusters of 3–5, perhaps hedging their bets against the loss of lone eggs. In contrast, small tortoiseshells, large whites and peacocks are unusual in laying largebatches of about 100 eggs.
However they are spread out, a female lays around 100–200 eggs. Mortality is often very high, but there is also the potential for a 100–fold population increase in a single season. This fecundity is part of insect success across the planet.