Where are all the butterfiles this spring/summer?
I haven't seen one Tiger Swallowtail butterfly or any other butterfly around anywhere except for a few small white cabbage butterflies. I have a butterfly bush in my backyard, that is normally covered with butterflies, but not this summer...I haven't seen any. I don't use any pesticides or anything else in my yard. I let nature handle everything. Is the lack of butterflies due to climate change or from people using neonics or a combination of both? It is very depressing not seeing butterflies around. :(
Montgomery County Maryland
We understand it's depressing and this is a common question we receive this time of year. The answer is complex, but in short, it is likely a combination of temporary seasonal fluctuations as well as chronic long-term issues.
It is good that you avoid pesticides; unfortunately, there could be many other reasons (perhaps multiple reasons at once) that are causing an apparent decline in your local butterfly population.
loss of habitat - while your yard flora is probably stable, public-land and private lots are not, alas, given continued development and the replacement of lost plants with non-natives (often) or plants which happen not to support the butterfly species in that area; most species are quite host-specific and have a relatively small range of caterpillar food options. Invasive plant species also displace native host plants, and deer (which avoid most invasive species) have become overpopulated and are consuming proportionately more native species than they used to. While they cannot reach mature trees (a food source for multiple butterflies), they can stunt or kill saplings that are needed to replace trees dying of natural causes in the woods.
use of pesticides elsewhere - we do not have precise data on how far various butterfly species fly and disperse, but blanket sprays for other pests (mosquitoes, Gypsy moths, etc.) can impact butterflies if the pesticide is not chosen wisely (or it's not possible to eliminate non-target impacts like this)
predator/parasite population dynamics - prey species and their predators (or parasites) can have "boom" and "bust" years, and tend to be cyclical, the peaks chasing each other as one population rises and then the other; winter and spring weather may play a role in survival of both species as well, possibly tipping the balance any given year
loss of host plants - as one example, the invasive pest Emerald Ash Borer has decimated our Ash tree populations, and Tiger Swallowtail uses Ash as one of its caterpillar host plants. We do not know if Ash plays a critical role in their life cycle (as they can use other species as well), or if Ash conveys any improved survivorship of caterpillars for some reason, but it is an instance of a supporting host plant no longer being widely available to a species. In addition, as mentioned above, several canopy trees play host to multiple butterfly species. Home landscapes, neighborhood street trees, commercial property grounds and so forth don't always plant these large species, instead opting for smaller and/or more decorative flowering trees that don't support the same (or any) butterfly larvae. For example, Hackberry trees support several butterfly caterpillars, but because Hackberry happens to have a horrible public-relations name and no particularly showy flowers or fall foliage color, it isn't planted as often as, say, the smaller and colorful Crepemyrtle, which supports none of our butterflies.
insufficient nectar sources - populations of some native "weeds" that grow primarily in disturbed sites, like Common Milkweed, can be mowed-down by maintenance crews when growing by roadsides (as presumably they are required to keep that shoulder buffer accessible) and in other unkempt wild areas near developed lots. Even though adult butterflies may get by using other nectar sources (Butterfly Bush, etc), perhaps these sources are not providing the same nutrition and therefore the reproductive health of the population is compromised.
timing - although butterflies tend to have multiple generations per year, the periods when most are in their non-adult life stages cause a lull in adult butterfly sightings; overlapping generations can occur, but as we approach late summer, more of the species that overwinter as larvae or pupae are prevalent as adults because they are in their final throes of breeding for the year. This tricks us into assuming butterflies are lacking in mid-summer when they may not be.
- population decline - sometimes it's just because populations are really on the decline overall, and this is blamed on a number of co-occurring factors which we touched-upon above: primarily habitat loss, pesticide use, and freak weather events. How much climate change is involved is still being studied. Generalized insect studies (and even anecdotal observations) in various countries have noted an apparent substantial decline in insect populations overall.
Thank you for your very informative answer. It makes me very sad to see the natural world in decline, due to human activity. Every time I see a forest around here being bulldozed, to make way for more houses, condos, parking garages, etc., it makes me want to cry. When I grew up in this area, there were an abundance of forests, butterflies, birds and other animals....I really miss those days. Also back then we never had to worry about Lyme disease because it was unheard of around here...but now it is a huge concern because Maryland is considered one of the hot spots for Lyme disease. (sigh)
You're welcome. You are certainly not alone in your sentiments about this. Keep doing what you can in your garden and in your community to support the habitat and conditions these insects and other wildlife need.