This evening I discovered an abundance of big ants in the basement of the home where I have lived big ant free for 15 years. Do I need professional help?
You can try ant bait, which will work on a lot of ants, but not all. I’m not sure what “big ants” are or how big these ants appear, but if they’re really big they may be carpenter ants (esp if wood is available) which are not easily gotten rid of with amateur level tools.
I’m pretty sure they are carpenter ants. They are definitely carpenter ant sized.
Is there wet wood somewhere either inside or outside? IME once you get rid of the wet wood, they will go away.
We were at a rental in Alaska once and used the fire pit at dinner. That night, the house was swarming with carpenter ants – like in a horror movie. So also consider if anything was disturbed outside.
You know what ants don’t do? Touch cucumbers, even though they grow on the ground.
My 96 yr old gran taught me this when I lived in an apartment infested with them. It was easy to see why, near the kitchen door, in the old house, the hardwood had plenty of gaps, as did the cupboards etc.
Gran said peal a cuke, slide the skin into the gaps and cracks and they’ll go away. But it won’t kill them. I really liked that part.
I bought two very long cukes, there were SOOO many gaps etc. and set about doing it!
(Gran assured me the skin would dry out, not mould, and continue to work. Gran lived in a virtual shack, and raised over a dozen children, so I figured she knew such things.)
Never saw another ant in that kitchen, and I lived in that apartment for three more years. I know all old timey remedies deserve healthy skepticism, but it DID work for me, and well.
Cucumbers are cheap, non toxic, and won’t kill the ants, maybe give it a try?
Good luck!
The first thing to do is get rids of points of entry. Walk around the house and make sure there are no branches growing close to the house. Fill any holes or gaps with spray foam. Then you want to observe them to see if you can identify a trail. Obviously remove any food sources, and then place ant baits in areas they congregate. Large ants are not necessarily carpenter ants, but if you find wet wood or a pile of wood dust you may have found the nest. Give the ant bait a few days and resist the urge to crush the ones you see - you want them to take the bait back to the nest to feed the colony. If you do find a possible nest spot inside the house, you’ll want to hire an exterminator to spray once a year or so.
Yes, or do you have a tree on your property that may be ill and compromised? Years back, I had an army of carpenter ants on my property. I would poison them periodically but, like the mongol hoards, they would keep returning in waves.
I had a beautiful willow in my back yard just 15 feet from my back deck but, unbeknownst to me, it was ill inside and compromised. It actually collapsed, and I had to have it all removed, the stump removed, and the hole filled. Magically, the carpenter ants disappeared.
No wet wood that I’m aware of (inside or out). We’re in a drought, as a matter of fact, though it looks like rain right now. No obvious points of entrance. I suppose there could be cracks in the foundation. The basement walls are all drywall.
If you know where your pipes are, check those areas. Sometimes wood framing is wet because of a small leak or condensation on water pipes behind the drywall.
As best you can follow the ants to where they are going. Once you figure out what they are after, you can deal with it. They are there for a reason; remove the reason if possible.
It seems like a lot of insects are especially active this year. I saw a bunch of complaints about biting flies along Lake Michigan this week and the cicadas are really buzzing loud. I noticed a few ants on my desk at work on Monday, an alarming number, 25-30? on Tuesday, a few yesterday and, today, I’ve only seen one in an hour, I think they’re done. I’ve sat at this desk for 9 years and get the occasional flying bug or a silverfish in here but don’t recall any ants before this week.
Call the Pentagon, they have nukes! 
Get three of these.
Use them.
They don’t seem to be going to (or coming from) any particular location. They are heading all directions, mostly on the floor but also on the walls. A few have found their way upstairs.
A recent thread:
Could be Argentine ants. Non-destructive to structures, but they are a pain in the ass to get rid of. Don’t really respond to the normal Terro borax solution stuff. My MIL had them in Indiana. Just showed up one day. Didn’t distribute in lines, it was mostly individuals exploring independently.
At our old house, I found carpenter ants walking across the coax cable connection from the neighbor’s yard. The neighbors had a tree that was mostly dead; once they removed it, the ants went away.
It’s been decades, but I seem to remember noticing them “commuting” at dusk. The rest of the time they were walking around randomly.
Good choice. Also good is Boric acid, which can be bought in a similar plastic dispenser called “Roach-Pruf” or somehting like that.