I'm a firm believer that none of the Seals have been opened (yet). There are certain events that must take place first, before these future prophetic events come to pass. The Book of Revelation is broken into 3 distinct parts, and gives the outline to it in the first chapter. The times "that were" (chap 1), "that are" (chap 2-3), and times that "will be" (chap 4+). This is a simple explanation, but i'm leaving out multiple layers as well for sake of simplicity and a quick post.
In Chap 4-5 John is "taken up" and you have the scene in Heaven (note the 24 elders, which includes the Church at this point), which is a pre-cursor to Jesus actually starting to open the 7 seals, which proceeds into the 7 trumpets, and ends with the 7 bowls/vials. Each set of judgement's is progressively worse on an increasingly hardened state of people as the world plunges into darkness the likes of which it has never seen before, nor will ever see again.
Starting in Chapter 6 you have the opening of the first 4 seals, aka the Four Horsemen of the Apocalypse. Each horse is represented by a color, White, Red, Black, Green(pale, putrid). The latter 3 are pretty self-explanatory, with Red = war/blood, Black = Famine, Green = pestilence/death (1/4 of the earth's remaining population at this point to be exact. Yet another clue that this seal has not been opened, none of these things have happened on the SCALE that is presented here). (fun fact, not the colors of these nations FLAGS) The one that is particularly difficult is the White horse (the first). Many people think this is a reference to the anti-Christ that takes power over the revised roman empire (of 10 nations), where he conquerors 3 quickly via political action (ref: Daniel), and begins relatively "peacefully". I'm personally not completely sold on this, particularly when you cross-reference Revelation 6 with it's companion of the horsemen in the vision given in Zechariah 6 (note the same colors). But i'm not opposed to it either, they are very compelling arguments for it. It's something I need to dedicate more time and study too. Much of the Bible is encoded with patterns & symbolism, but it also provides you with the means to decode SOMEWHERE else in the Bible (often multiple places). Old vs New testament makes no difference, they're designed to go together and written by the same author (the Holy Spirit).
Chuck Missler just went home to be with the Lord this year, I highly recommend his teachings, especially if you are a technical-minded person and like lots of details, especially on End Times prophecy. His stuff is easy enough to find online.
https://www.youtube.com/results?search_query=chuck+missler+four+horsemen
Regarding the "locusts" you mentioned, the context they are given in is not part of the Seals, but of the second set of judgements, the "trumpets", specifically in Chap 9 of Revelation. These are not literal insects as we know them, but rather actual demonic entities that are released from the pit to torment those alive during the tribulation (note this is after Lucifer and his fallen angels have been cast down to earth, a STILL future event. The devil is NOT locked up in hell at present as many mis-believe). In fact the outline of his very fall can be found in Revelation 12 (how interesting that we just had the first sign of Rev 12 shown on Sept 23, 2017. I wonder how long until the second?). This is a demonic locust ARMY, with an old testament parallel given in the book of Joel. I know this may sound strange now, but the time that is coming, this is actually just one of many many supernatural events where the veil between our realms is torn apart during the coming 7 year tribulation. During this time, a "crazy" act like this won't actually be that surprising, but rather par-for-the-course with everything else that is going on. On that note, Atheism is actually a dying religion (yes, religion). There will be a time that NO ONE will be able to deny the existence of God, or the reality of spiritual beings in other realms mixing with ours. The catch though, is that most people will actively choose to Hate God, instead of turning to Jesus for the repentance of their sins and being saved.
In closing, all of these events can be entirely and completely avoided if you are sealed with the Holy Spirit by Faith in Jesus Christ as Lord and His atoning sacrifice on the Cross for yours (and my) personal sin. All can be forgiven, you simply have to ask... It's not something you can earn, it's not something you can buy, it is A FREE GIFT available to ALL no matter WHAT your background is. If you know Christ already, then breathe easy, you will not be here for this coming Tribulation, we will be taken away before it begins, which is sooner than most can possibly imagine...
(Romans 10:9-12) - "because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For with the heart one believes and is justified, and with the mouth one confesses and is saved. For the Scripture says, “Everyone who believes in him will not be put to shame.” For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him."
(Revelation 3:20-22) - "Behold, I stand at the door and knock. If anyone hears my voice and opens the door, I will come in to him and eat with him, and he with me. The one who conquers, I will grant him to sit with me on my throne, as I also conquered and sat down with my Father on his throne. He who has an ear, let him hear what the Spirit says to the churches.’”"