For nearly 30 years, the Monarch Larva Monitoring Project has counted monarchs during the breeding season throughout the butterfly's range. Usually, there are two peaks in monarch numbers: one in late May, and a second, larger peak in July. This year, the second peak is much smaller than usual--smaller than the May peak. You can see graphs of monarch numbers this year, compared to other years, at this link, thanks to Karen Oberhauser.
What happened? Dr. Oberhauser said: "A possible cause is the big rainstorms just as generation 2 was about to eclose. Adult monarchs are good at hunkering down when it’s raining; they can’t lay eggs, but they can generally find shelter and wait the rain out. And we don’t have good evidence that normal rainstorms wash eggs, larvae, or pupae off plants (although this hasn’t been well-studied). But eclosion from pupa to adult is a vulnerable, albeit short, event, and monarchs probably can’t delay it to wait for better weather. The intense heat early in the summer may also have affected both eclosion success and butterfly fitness."
Numbers might rebound in August, though this is unlikely. Probably the August population crash will result in lower numbers of monarchs in Mexico this coming winter.
Consequently, Monarchs for Kids needs to adjust our egg production methods so we remove fewer wild monarchs from the population. We may select one or more of these options:
- Provide fewer eggs per class. In the past we've provided 10 per class. We may drop this to 5 or even 1.
- Capture fewer wild females for laying eggs in captivity, or release them after they have laid a small number of eggs.
- Rely only on females we raise from the egg. Most wild eggs are eaten by predators before they hatch.