Survival Guide: Army Cutworm Moth Edition

Army Cutworm Moths (Euxoa auxiliaries), like a lot of insects, are very proficient reproducers. In fact, individual females can settle into the soil and oviposit, or lay, anywhere from 1000 to 3000 eggs (Burton et al. 1980). This release of eggs marks the end of a long, spectacular journey for the adult moths. Soon after laying the eggs, the adult moths will die. However, this only happens if they don’t die sooner.

Whitney Cranshaw, Colorado State University, [CC BY 3.0 us (], via Wikimedia Commons

Whitney Cranshaw, Colorado State University, [CC BY 3.0 us (, via Wikimedia Commons

Here’s a list of advice to these moths to stay alive as long as possible:

1. If you can, stay at lower altitudes.
Also called Miller moths, they typically range in length from 1.5 – 2 inches and have an average wingspan of 1.5 inches. They are holometabolous, meaning they go through complete metamorphism. This includes four stages of development— an embryo, a larva, a pupa, and an adult. This is important because having different juvenile and adult forms allows the army cutworm moth to occupy different ecological niches.

These moths overwinter as larvae in the midwestern states. In the spring, they begin feeding on plants such as alfalfa and smaller grains. Pupation occurs underground after a total of 6-7 instars from egg to last molt (Snow 1925). Finally, the adults emerge in early June and migrate west into the Rocky Mountains. It’s this migration that is quite phenomenal and has left researchers scratching their heads.

Presumably, the moths migrate to avoid the high summer temperatures. They also tend to migrate upward in altitude as they seek sources of energy-rich nectar. This increase in altitude leaves them exposed to intense sunlight. It also puts them in the same ecological space as grizzly bears, which also make the trip to higher elevations during the warm summer months.

Note to the moths- You may starve if you stay at a lower altitude because of the lack of food. But, you’re probably going to die if you travel up the mountain. Choose wisely.

2. Find somewhere else to hide besides on the ground.
Because of the intense sunlight, the moths will feed on flower nectar at night and hide in dark crevices during the day. These dark crevices are usually underneath the accumulation of piles of rocks. The bears will dig through and flip over large rocks (nothing for a grizzly) to expose and eat the moths.

While hiding during the day, the moths will metabolically transform the nectar into fat and even increase their body fat by 60% over one summer (Kevan and Kendall 1997). Therefore, the moths are extremely important to grizzlies during the summer and early fall months.

Note to the moths- Maybe you could find another dark place to hide. If you can find a tree at that altitude, that may work. However, with Clark’s nutcrackers flittering about, you may meet the same fate.

3. If you must hide under rocks, don’t follow the crowd!
The problem is the moths do not take cover individually, but in aggregations by the hundreds of thousands. Experts estimate that grizzlies can consume around 40,000 moths per day and close to one million per month (White et al. 1999). The reason for this consumption rate is because, for grizzlies, finding one of these sites is like finding several meals. The moths provide an important fat source for the grizzlies, especially since their other major staple food, the white bark pine nut, is disappearing. If one grizzly eats one million moths per day, this would actually account for 47% of that bear’s annual caloric budget.

Note to the moths- This might be your best chance. Being a loner could actually benefit you. I know you must feel pressure to follow your friends, but don’t give in to the temptation. Statistically, it doesn’t look good for you if you follow the crowd.