As the story goes........
Three perfect male Monarchs emerged from their chrysalis's yesterday. It was a lovely day for them to fly - sunny with a light breeze.
The first two emerged early in the day and by late morning had flown off.
The third male emerged from its chrysalis, a good hour after the others, so was still around into the afternoon. Eventually he too was ready and flew into a nearby bush.
Without warning an old male (its wings were very tatty) flew into the garden. It flew directly to the bush and attacked the third butterfly. The old male just clamped itself straight onto the back of the other and there was quite a tussle. The new male could not move much at all and was writhing to get out of the other's grip.
Fortunately I observed this event and was able to reach them and somehow get them apart. The old boy flew off and the new boy flew higher into another tree and remained there for several hours.
The old boy soon returned and continued to circle the garden but did not repeat the attack.
It's a known fact about Monarchs, and other butterflies, that the established males just do not like young males coming onto their patch.
Check out this interesting article about battling butterflies in Science Daily.
My favorite activity while I'm inside is to look out of the window overlooking the butterfly/hummingbird garden on NE sideyard of the house and see what, if anything, is going on. I also have another favorite window overlooking the SE backyard.
Until even a few days ago, Monarchs coming into the garden have mostly been travel-worn tattered and faded butterflies, but I'm seeing more and more fresh and bright, newly eclosed ones.
So it's been quite interesting to see how the males tend to fly in almost a patrol pattern all over the garden -- not just over the Butterfly garden but also the back yard -- I guess because there are sparse milkweed patches nectaring flowers in the back as well as the other sideyard as well, and my side and back yard are well-defined by the white fence and the woods bordering the back fence... and the butterflies seem to recognize these boundaries.
What I mean is, the male Monarchs will fly a patrol pattern within those perimeters and chase off any other males to just outside of the fence. Having been chased out, the 2nd butterfly will attempt to fly back in, and get chased off again, over and over... Then sometimes, they get smart and fly along the fence on the front yard side and then either cut in just before reaching the house, or, sometimes, fly on across the front of the house, then sneak back in from the other side, just to be chased back out again when the patrolling male reaches that side. They will go after any other butterfly nectaring at their favorite stations, including cabbage whites and skippers, not just the larger ones like Black swallowtails or Tiger swallowtails.
I've seen this behavior explained as lusty, grab anything and try to mate brute action on the part of male Monarchs, but that doesn't fit what I have been observing.
This morning, I saw two males in mid-fight/flight change vectors and together chase off a hummingbird that was nectaring at the A. tuberose milkweed patch. I was wondering if I imagined it, when the hummingbird flew back to the flowers, only to be set upon by the two males from two different directions!
REF: HELPFUL GARDENER