By PATRICIA SIMPSON
This month’s observation of the month is an observation of a moth. Say that 10 times fast! iNaturalist extraordinaire klyle161 was lucky enough to spot a magnificent Ceanothus Silk Moth (Hyalophora euryalus) which can be seen at bit.ly/3bAB5fG
While this species is not particularly rare in San Diego County and despite its large size (roughly the palm of your hand), it is not often seen. One of the reasons for this is the short life span of the adult moth — one to two weeks. Why so short? The adults of the Saturniinae subfamily (Giant Silkworm Moths) emerge from their cocoons without any mouth parts. Without the distraction of having to find food, the sole purpose of these night critters is procreation.
The male, adorned with two large antennae, is equipped to detect the female’s pheromones (chemical scents). He will fly around until he finds a mate.
In contrast, after emergence the female will stay put and wait for a male to find her. After all, she needs to save her energy for her post mating job — laying eggs. She first has to fly around and pick particular host plant species suitable for the “kids” which includes (you guessed it) ceanothus. If she lays her eggs on the wrong plant, the caterpillars will not survive.
Even though she will lay more than 100 eggs, she will fly to many different host plants and only deposit a few eggs on each one. The caterpillars are voracious so they can’t all be on a single plant. With mating and egg laying duties completed, the adults reach the end of their lives.
From the eggs will hatch tiny caterpillars. They will not be small for long. They will feed on the leaves of the host plant and in a matter of a few months will grow to roughly 4 inches. Just imagine fat sausage-like green fingers with yellow and black spikes!
When it is time to pupate, they will crawl to a different plant, build a cocoon and pupate inside of it. The reason for leaving their feeding ground is simple: avoid predators who would surely hunt them down after seeing the decimated leaves and frass (insect poop), all sure signs of a tasty grub nearby.
In the cold of winter, the pupa will enter diapause (resting phase) until temperatures warm up and are suitable for the adult to emerge and spread its large wings. And the cycle starts all over again. But wait, which came first: the egg or the moth?
To see the 80 observations of Ceanothus Silk Moth in San Diego County since 2015 in iNaturalist and see photos of the different life stages, visit bit.ly/2JmMio6
— Patricia Simpson is a trail guide at Mission Trails Regional Park.