Swallowtail Butterflies


Several weeks ago, we had orange and black Monarch butterflies migrating through the Front Range. They seem to have moved on.

But we’ve still got big butterflies in the area — yellow and black swallowtails. I’ve seen two different types of swallowtails. The western tiger swallowtail is lives along waterways and in woodlands, as well as suburban areas. It’s caterpillers eat aspen, cottenwoods and green ash. The eastern version of this butterfly …. hmmm…. lives in the east? That’s all I’ve found to separate the two.

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Western tiger swallowtail on Canada thistle.

The other species of swallowtail that I commonly see in the west Denver area is the two-tailed swallowtail. Predictably, it has two tails.  These butterflies lay their eggs on green ash and chokecherry, although the adults evidently like the nectar from our milkweed plants.

Two-tailed swallowtail
Two-tailed swallowtail on milkweed.

It’s a hard life being a butterfly. This poor guy has survived a lot.

Damaged two-tailed swallowtail butterfly on milkweed.

Swallowtails lay their eggs on their preferred plants. The eggs hatch out into caterpillers, which proceed to feed on their host plants. When winter comes, these larva spin a chrysalis (cocoon), in which they overwinter.

Unlike Monarchs (Monarch Butterfly Migration) or Painted Ladies (Painted Ladies migrate across North America! Painted Ladies Part Two), swallowtails only produce one generation a season. The adult swallowtails emerge in May and June, and continue to be active in the same area through August, feeding on plant nectar, as the butterflies above are doing. Sometime in the summer, they lay their eggs.

6 thoughts on “Swallowtail Butterflies

  1. Great blog, wonderful pictures and interesting information. I’ll share with The Ladies, and I”ll tell them about your 4 foot milkweed plant, growing through the concrete crack.

  2. Pingback: Butterflies | Colorado In Depth and At Altitude

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