What we need here is a picture that is not backlit, it removes all the detail from the insect.
Try a flash photo or shine an LED or other flashlight on it.

The insect is of a size that if attracted to lights, it could squeeze through the mesh.

I played around with the image and can only speculate that it is a moth or bug, not a beetle.

I was going to say June bug/May beetle/June beetle, but if that screen has the grid size of a normal window screen, then the size would be way off. HA! What is the approximate size? As tiny as it seems?

"Wing" portions may be artifact of the photo/quality/lighting. Note halo around all gridlines in this expanded image. But it does give the impression of incompletely tucked beetle wings.

Thank you so much for everyone's comment! I'll wait till it appears again to take a much better picture for identification.

Yes, the bug is only a few mm big. Maybe 3mm long?

Hopefully this time the pics show more. I crushed the bug though. The bug is very small, about 3mm long.

Here is the back of the bug

Where is the apartment located? US? What city?

Around New England for a decade or more now, I've noticed lawn chafer beetles (European lawn chafer beetle, I believe it is.) They are everywhere there are lawns in late spring, early summer. They are attracted to lights and I sometimes find them between the screen and window or inside the house (if doors are opened when say a porch light is on or they come off a screen and fly into the house). Oftentimes they will be hanging on the outside of a screen. Here is a link that might be helpful:

https://en.wikipedia.org/wiki/European_chafer

That particular chafer is 1/2 inch or larger, much bigger than the 3mm (1/8") described for the unknown.

Does look beetlish but cannot rule out bug, I have enhanced the above images:

The apartment is located in NYC. I am surprised to see them when all the windows are closed, so I don't know where they came from. If need better pics, I can try to take another with better sunlight tomorrow.

Lighting is not a problem, the images can be manipulated for that; it is detail that is lacking for a nondescript insect. The picture would need to be taken from 2 or 3 inches away, using macro settings.

Appears too small for a roach and not flat enough for a bedbug, so there is two varmints eliminated.

Looks like a June bug

OK, I finally encountered another one. This time I used my camera to take a picture of it. Hopefully this time is better. This bug is slightly bigger, about 5mm. Again, I closed all my windows and I have no idea where it came from.

Similar to certain larder beetles, see:
http://www.uark.edu/ua/arthmuse/blklarder.html

If dermestid, the beetles may be coming from within the house or apartment building in general. There are lots of different larder beetles.

I have more pictures. One is dried and the other one I just killed:

Found another one between the window and the window screen, I am not sure how it got there:

I think it's a kind of beetle too. Questions:

1. How can I prevent them from entering my apartment or how did they get in between the screen and the window?

2. What is their food source? I want to make sure nothing in my apartment will attract them.

Ken,

When I first saw your post and beetle like bug, I was taken back some years ago when, I'll and fatitigued for months, I finally "woke up" to an infestation of a type or larder, tobacco, or "drug store beetle." I was DENSE or Obtuse because I was ill; otherwise it would have grabbed my attention and I would have quickly figured it out.

My beetles and ((ultimately) their larvae, were in my cupboards over the sink and sometimes falling down onto the countertop (white). I was I'll and extremely fatigued and preoccupied, so, hard as it might be to imagine, the beetles and larvae did not "register". I am a life- long observer of natural history -- critters, insects, plants, marine life and birds. That I failed to take sharp note, is testament to how weak and ill I was.

After some months, it "registered" that this phenomenon was a pest. This was back during the pre-spa irked UseNet days. I asked/posted about it and got some ideas. Months earlier, I had noticed that a cellophane-packaged bunch of dried red chilies had become skeletonized/ moth eaten looking. I was experiencing enormous fatigue and pain and being treated roughly by various capitation incentivized HMO doctors, even though there was real injury. My mind was elsewhere.

The report back from the science oriented usenet folks (several were entymologists) was that I had an infestation of something like "drug store" or "tobacco" beetle.

I sort of came alive with a bit of panic-induced boost ;)

I cleaned out my cupboards of things like paprika, dried parsley, on and on.

The larvae of these ~ .25 to .5" or smaller reddish brown beetles were nearly everywhere. In jarred goods, somehow threading along the grooves of the screw on caps of the paprika. In the dried pasrley. In the cracks of the cupboards itself.

I did not want to use any pesticide in my house, kitchen, or cupboards. I was exhausted, but spent s days washing, tossing spices and herb bags into the outdoor bin (freezing temps), and using a powerful vacuum cleaner with small straw-like attachments.

I think this was before the widespread a availability of digital cameras, but IIRC I did get photos or scans of them. A grad student across the country begged me to send her some of the beetles (they did not seem to readily fit into any of the usual suspects). I was too exhausted, but also didn't think that it would be smart to attempt to mail even dead specimens to the big agricultural state where the post doc lived.

It took a while to get rid of them. Exhausting. Now, if I buy any ethnic market or health food store grains or spices, I put them into my freezer for two weeks. Sometimes (as with whole wheat flour) I just keep them in the freezer.

I think our bug guy, Larry, is in the mark. It looks like you have a pantry or larder beetle. If you have not already done so, it might be wise to put any grains, chilies, herbs, pasta, flours, or spices or chilies into glass jars with tight fitting lids. Freeze them for a few days, or toss and replace. Keep cleaning your cupboards and storage areas. Toss the vacuum cleaner bags outside in the trash bin (not inside).

Best of luck to you.

The larva of these beetles sheds its skin, leaving behind a small, dry, bristly thing. I see those more often than the actual beetle.

That appears to be a woven rather than a welded screen; beetles are very strong and could force their way through the weave. See if poking a pencil tip widens a screen square.

Food in opened, original packaging such as cereal boxes, plastic bags, etc. are best stored in tightly-lidded plastic containers, if insect pests are present.

Clothing and textiles made from natural materials are also a food source.

See Cigarette Beetle (and also click the link for drugstore beetle for a comparison.
http://entnemdept.ufl.edu/creatures/urban/stored/cigarette_beetle.htm

Antennae would be wrong and elytra do not appear to be hairy, but given the quality of above images and rough handling of some of the specimens, the latest ID is possible.

Perhaps Ken has a stash of cigars.

Thanks, Jean, for the link. It was a long time ago that I got my beetles, but those photos of the drugstore beetle with the linear pits resonated. They hijacked their way in with some dried red chili peppers. Blech! That was one ugly experience.

Ken, you can always put the beetle in a jar, then put the jarred beetle into the freezer for a day or a few years >g<

Larry, were you thinking that perhaps Ken's beetles are "entering" (via the woven screen)? Here is my name for a new product: Beetle Bye. There is an app and an analyzer. You introduce the pest to a vial connect to a spectrometer gizmo and app. Any critter with the image and chemical and DNA gets hunted down and vaporized.

I've been assuming it is an interior screen and indoors beetles were forcing their way through it.

That is what I was wondering too. And they would want to get to the outside...

-- because they are attracted to fresh air and light?

-- they miss their relatives?

-- want to find more foodstuffs. Ken's is used up or sealed up?

First of all, I don't have a stash of cigarettes. :P

Second, my previous apartment was infested with Indian moth so I actually bought a lot of air tight OXO containers for all my dried food since then. Plus I freeze every dry stuff from grocery store in the freezer for a week before storage. In addition, I don't see these bugs very often. Maybe one or two per two weeks during spring-summer months. Moreover, I found it between the window screen and window (and I don't ever open that window, and the screen is located outside. I took the picture inside my apartment with the window pane in between my camera and the window screen).

Hence I believe it's coming from my neighbors. I don't know what I can do in this case. They could be coming from cracks and nooks.

Since this topic began with "I have been seeing this bug in my apartment for some time now.", we have been operating on the wrong premise.

Yes, "I have seen the bugs for some time now" = I saw them during the spring/summer months for the past 2-3 years now. I procrastinated from identifying the bug until now since they don't seem to bite, nor I could see any "physical" damages.

Actually I see one or two every week (as opposed to every two weeks as written above) for the past 2-3 years during spring/summer (usually from April to Aug).

"Hence I believe it's coming from my neighbors. I don't know what I can do in this case. They could be coming from cracks and nooks."

Hmm, that might explain it. But if so, I wonder why they haven't noticed.

Time to move again, Ken :-/

I had to look up "Indian moth" ....

Is that the name of the "pantry moths" that can infest bird seed, dog kibble? I had an apartment in the country once and naively stored bird seed in the kitchen in its bag. You can guess the rest. The larvae can eat right through a zip lock (thick poly) bag. I had to toss everything, and vacuum until there was no air left in the kitchen. Horrible.

You food storage system sounds smart.

Indian Meal Moth is the specific pest species common name; there are other pest moths of stored food.

No bites is very good news, but one doesn't want unknown bugs around.

Some kind of pantry pest beetle, can't tell which one from the photo.

They are not poisonous to eat. Give the remainder of this pizza to Bear Grylls.