How do you tell the difference between a male and a female Monarch butterfly?

Question Answered by Cory Braastad, Biological Field Technician, INL ESER Program

If you have a flower garden at your house there is a good chance you have seen a Monarch butterfly floating around. As you are watching them you might wonder how to tell the difference between males and females. They are the same color but there is one difference that you might see is that there are little black spots on the bottom of the wings of the males. Males have black spots; females do not. The best way to get a good look is to wait until they land on a plant or netting them with a butterfly net. You can get a good idea of what the spots look like by looking at the pictures below. The spots on males were once thought to be scent glands, but they are actually vestigial (an organ or body part that continues to exist without retaining its original function, such as our appendix) and no longer serve that purpose.

Western Monarchs

US Fish and Wildlife Service

There are two distinct populations of monarch butterflies (Danaus plexippus spp.) in North America. Western monarchs range west of the Rocky Mountains and winter in the forests of coastal California.

According to USGS scientist, Jay Diffendorfer, Western monarch butterflies dropped by about 97% of their average historic abundance between the 1980s and mid-2010s. In winter 2018–2019, the population plummeted even farther, to fewer than 30,000 monarchs, which represents a single year drop of 86% and a drop of about 99% since the 1980s. The population may now be hovering at its quasi-extinction threshold.

Loss of milkweed needed for monarch caterpillars to grow and develop is one of the reasons for their decline. Drought conditions in California, the monarch’s wintering grounds, have reduced the amount of milkweed available. Plus, many insect pollinators including monarch butterflies and monarch larva are affected by pesticides, which are designed to kill harmful insects, but often also kill beneficial insects like pollinators.

Pollination is the process by which pollen from one plant is moved to another plant of the same kind. When this happens, the plant is able to make new seeds.

Some plants produce a lot of tiny, light weight pollen. These plants rely on wind to spread their pollen. But, most plants have larger, heaver, sticky pollen which require an animal to move pollen.

Pollinators can be many different kinds of animals, but most often they are insects. Pollinators are really important in producing many of the foods we eat. Strawberries, bananas, apples, blueberries, almonds, cashews and chocolate all require the help of a pollinator to be produced!

Plus, many wildlife species need pollinators to help produce their food, too. But many of our pollinators are declining in numbers.

Be a monarch super hero! Try some of these simple, but important, steps to help conserve our monarch butterflies.

  • Plant milkweed! Monarch caterpillars need milkweed to grow and develop.
  • Plant butterfly nectar plants! Monarchs need nectar to provide energy as they breed, for their migratory journey, and to build reserves for the long winter. Some monarch garden plants are chives, wallflowers, salvia and cosmos .
  • Avoid using pesticides when possible.

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