3 August 2023

After Wednesday’s report on the scarcity of monarch butterflies in southwestern Pennsylvania, yesterday brought happier butterfly news.

This week Donna Foyle and Betty Rowland both found black swallowtail caterpillars (Papilio polyxenes) on host plants in their gardens. Donna Foyle’s are on parsley. Betty Rowland’s are on fennel.

This success prompted a lively discussion of next steps.

#1. Birds, insects and spiders prey on black swallowtail caterpillars so the first step is to protect them. Birds are easy to exclude. Betty Rowland put a butterfly shelter over her fennel.

#2 What if the caterpillers eat all your host plants? Where can you get more? Well, don’t buy greens for your caterpillars! You can’t be sure they haven’t been treated with chemicals. Donna Foyle will look for Queen Anne’s (not near a road) if it she runs out of home-grown parsley.

When the caterpillar is ready to pupate it develops a somewhat camouflaged chrysalis, two examples shown below. (The brown one was photographed in Pittsburgh by Scott Detwiler.)

As adults, black swallowtails are sexually dimorphic …

… which is useful for their mating strategy.

The Papilio polyxenes demonstrates polyandry and a lek mating system, showing no male parental care and display sites. Females are therefore able to choose males based on these sites and males are the only resource the females find at these sites.

— Wikipedia: Black Swallowtail butterfly account

For loads more information about black swallowtails and photos of all their stages, see Wikipedia’s black swallowtail account.

31 July 2024

Have you seen any monarch butterflies this summer?

Twenty years ago this question would have been absurd in late July, but this year nature observers are worried that they have seen only one monarch butterfly so far … or none at all. There are two reasons why monarchs are scarce. One is the symptom, the other is the cause.

The Symptom: According to World Wildlife Fund, last winter’s annual survey of monarch butterflies on their wintering grounds in Mexico found that “the species occupied only 2.2 acres during the 2023-2024 winter season — 59% less than the previous year when scientists observed 5.5 acres.”  There are 59% fewer monarchs this year compared to last. UPDATE: See Christine Rickabaugh’s comment below with the backstory on what’s happening in Mexico.

The Cause: Since the 2010’s biologists have warned that we are experiencing an Insect Apocalpyse. They have declined an alarming 75% in the past 50 years. The reasons for decline have been hard to tease out because there are so many factors at work.

Fortunately scientists at Michigan State University conducted a comprehensive study on the effect of herbicides and insecticides on insects, and especially on monarch butterflies (Danaus plexippus), in the Midwest. Published last month in PLOS One the study collected recent and historical data from Wisconsin, Michigan, Iowa, Illinois, Indiana and Ohio. MSU Today describes the findings.

While habitat loss, climate change and pesticides have all been implicated as potential causes for the declining insect abundances being observed globally, this work was the first comprehensive long-term study to evaluate their relative effects. Using 17 years of land use, climate, multiple classes of pesticides and butterfly survey data across 81 counties in five states, the researchers found that shifts in insecticide use toward neonicotinoid-treated seeds are associated with an 8% decline in butterfly species diversity across the American Midwest.

These findings include the decline of the migratory monarch butterfly, which has been a prominent concern. Specifically, it is noted that insecticides rather than herbicides are the strongest pesticide factor associated with monarch declines.

— Michigan State University: Insecticides found to be primary driver of butterfly decline

Neonicotinoids are so deadly to insects because they are so pervasive. Applied to the soil or as a seed coating, they migrate into the soil, the plant, its pollen, the water table and the air. This diagram shows the transport of neonics as red dots. They are everywhere.

The biggest danger comes from agricultural use. In 2017 the percentage of soy and corn planted with neonic seed coatings (colors below) was high. Now it’s even more.

Neonicotinoids are so effective that they create places without insects. These biological wastelands are missing everything that depends on insects, all the way up the food chain. This cornfield is a wasteland. There are no bugs and no birds here.

And the sneaky part is that you may be putting neonics on your grass or in your garden without realizing it. If you (or your lawn care company) sprays your grass it may well contain neonics. The potting soil and plants you buy at the store are probably treated with neonics before you buy them. Suddenly your lawn and garden are deadly to the butterflies and bees you’re trying to attract. Read more about it in the PDF linked below (or here).

It is going to take a concerted effort from all of us to remove neonicotinoids from our environment and stop the decline of insects. The best time to begin is right now.

p.s. EPA proposed an interim decision on neonicotinoids to protect pollinators. Alas, it says they are proposing “management measures to help keep [neonictinoid] pesticides on the intended target.” Good luck with that. Neonics never stay in one place.