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Limiting Factors
Monarch numbers can rise and fall for countless reasons. Here are some examples of limiting factors:

  • Temperatures can be too hot or too cold;
  • Precipitation can be too high or too low;
  • Food Sources can be scarce or abundant;
  • Enemies can be many or few;
  • Diseases can be deadly or mild.

Milkweed
Will monarchs find a healthy supply of milkweed when and where they need it?

Fire Ants: by Mike Quinn, TexasPredators
Fire ants eat monarch eggs.
Mike Quinn, TexasEnt.net

Parasites
See the tachinid fly larva coming out of the chrysalis?