Caterpillars in Snapdragon Blossoms

2023 September 10

In early August, Sandy bought a bouquet of flowers from the local farmer’s market. It was mostly snapdragons. And on August 10, 2023, we noticed that there were little caterpillars living in the blossoms.

Small caterpillar

They were in a range of sizes, with little ones less than a quarter of an inch long, ranging up to larger ones almost half an inch long.

Medium caterpillar
Large caterpillar, with medium caterpillar draped across it

They all had obvious black spots in a consistent pattern, but as the caterpillars got bigger the spots stayed about the same size. The bigger caterpillars also got greener.

Medium sized caterpillar
Large caterpillar

They were almost exclusively confined to the vicinity of the blossoms, and were not eating the snapdragon leaves.

I’ve seen caterpillars with that pattern of spots before. The pattern is almost spot-on for the Carrot-Seed Caterpillars that I photographed in the past. Unfortunately, there are several reasons to think they are not the same species as the ones I am posting today:

  1. The spots on the carrot-seed caterpillar are larger relative to the caterpillar than we see here.
  2. They are different body shapes. The carrot-seed caterpillars are fat in the middle and taper a bit at the ends, while these are a fairly uniform diameter.
  3. Carrot-seed caterpillars eat seeds of plants in the carrot family. Snapdragons are not even in the same order as carrots, let alone the same family, so it seems unlikely that they would make such a big jump in their choice of host plants.

On the other hand:

  1. I have been searching for caterpillars that are known to eat snapdragon blossoms and that are spotted like this, and am drawing a big, fat blank.
  2. The carrot-seed caterpillars are well known for confining themselves to eating blossoms and seeds, which is what these are doing.
  3. The carrot-seed caterpillars also almost always show a broad spread in caterpillar ages, with both large and small caterpillars eating the same plant. Just like these are doing.

So, maybe they are the same caterpillar? Maybe some of them managed to jump hosts from carrots to snapdragons, and are now well on their way to becoming a new species. These things happen, so it is possible. But is it likely? That I can’t say.

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